Be aware that we prettify prices after conversion 😄 That code is quite long:

       if(!$specialRounding){
            //Major Tipping Points
            $majorTipped = false;

            switch ($result){
                case $result >= 89 && $result <= 111:
                    $result = 100;
                    $majorTipped = true;
                    break;

                case $result >= 890 && $result <= 1110:
                    $result = 1000;
                    $majorTipped = true;
                    break;

                case $result >= 8900 && $result <= 11100:
                    $result = 10000;
                    $majorTipped = true;
                    break;

                case $result >= 89000 && $result <= 111000:
                    $result = 100000;
                    $majorTipped = true;
                    break;

                case $result >= 890000 && $result <= 111000:
                    $result = 1000000;
                    $majorTipped = true;
                    break;

                case $result >= 8900000 && $result <= 1110000:
                    $result = 10000000;
                    $majorTipped = true;
                    break;
            }

            if(!$majorTipped){
                $resultBeforeTipping = $result;

                //Check Tipping Points
                $nearest_100 = round ($result, -2);
                $proximity = abs((($nearest_100 - $result) / $nearest_100)*100);

                if($proximity <= 4.5 && $result > 111.01 && $result < 889.99){
                    $result = $nearest_100;
                } else{
                    $nearest_1000 = round ($result, -3);
                    $proximity = abs((($nearest_1000 - $result) / $nearest_1000)*100);

                    if($proximity <= 4.5 && $result > 1110.01 && $result < 8899.99){
                        $result = $nearest_1000;
                    } else{
                        $nearest_10000 = round ($result, -4);
                        $proximity = abs((($nearest_10000 - $result) / $nearest_10000)*100);

                        if($proximity <= 4.5 && $result > 11100.01 && $result < 88999.99){
                            $result = $nearest_10000;
                        } else{
                            $nearest_100000 = round ($result, -5);
                            $proximity = abs((($nearest_100000 - $result) / $nearest_100000)*100);

                            if($proximity <= 4.5 && $result > 111000.01 && $result < 889999.99){
                                $result = $nearest_100000;
                            } else{
                                $nearest_1000000 = round ($result, -6);
                                $proximity = abs((($nearest_1000000 - $result) / $nearest_1000000)*100);

                                if($proximity <= 4.5 && $result > 1110000.01 && $result < 8899999.99){
                                    $result = $nearest_1000000;
                                }
                            }
                        }
                    }
                }

                //If not tipped - do general intervals
                if($result == $resultBeforeTipping){
                    if($result >= 17.5){
                        if($result > 17.5 && $result < 50){
                            $result = $this->roundToNearest($result, 5);
                        } elseif($result < 100){
                            $nearest_10 = round ($result, -1);
                            $distance = abs($nearest_10 - $result);

                            if($distance <= 3.5){
                                $result = $nearest_10;
                            } else{
                                $result = $this->roundToNearest($result, 5);
                            }
                        } elseif($result < 200){
                            $result = round ($result, -1);
                        } elseif($result < 1000){
                            $result = $this->roundToNearest($result, 50);
                        } elseif($result < 5000){
                            $nearest_100 = round ($result, -2);
                            $distance = abs($nearest_100 - $result);

                            if($distance <= 45){
                                $result = $nearest_100;
                            } else{
                                $result = $this->roundToNearest($result, 50);
                            }
                        } elseif($result < 10000){
                            $result = $this->roundToNearest($result, 100);
                        } elseif($result < 50000){
                            $nearest_1000 = round ($result, -3);
                            $distance = abs($nearest_1000 - $result);

                            if($distance <= 450){
                                $result = $nearest_1000;
                            } else{
                                $result = $this->roundToNearest($result, 500);
                            }
                        } elseif($result < 100000){
                            $result = $this->roundToNearest($result, 1000);
                        } elseif($result < 500000){
                            $nearest_10000 = round ($result, -4);
                            $distance = abs($nearest_10000 - $result);

                            if($distance <= 4500){
                                $result = $nearest_10000;
                            } else{
                                $result = $this->roundToNearest($result, 5000);
                            }
                        } elseif($result < 1000000){
                            $result = $this->roundToNearest($result, 10000);
                        } elseif($result < 5000000){
                            $nearest_100000 = round ($result, -5);
                            $distance = abs($nearest_100000 - $result);

                            if($distance <= 45000){
                                $result = $nearest_100000;
                            } else{
                                $result = $this->roundToNearest($result, 50000);
                            }
                        } elseif($result < 10000000){
                            $result = $this->roundToNearest($result, 100000);
                        }
                    }
                }
            }

            //Cast to int if it's not already rounded by now
            $result = (int)round($result,0);

            //Final Currency Adjustments
            if($rate < 1 && $result != 0){ //High value currencies (EUR/USD etc)
                if(($result % 10) == 0){
                    $result -= 1;
                }
            } elseif($rate < 4 && $result != 0){ //Medium value currencies (NOK/SEK etc)
                if(($result % 10) == 0){
                    $result -= 1;
                }
            } elseif($rate > 10){ //Low value currencies (HUF etc)
                $result -= 10;
            }
        }