Unexpected round() return
$line_item_price = 13.775;

echo round($line_item_price, 2, PHP_ROUND_HALF_DOWN);

$line_item_price = 13.775;
echo floor($line_item_price * 100) / 100;

echo round($line_item_price, 2)

$num = 13.775;
$tmp = intval($num*1000);
$dec = $tmp % 10;
if ($dec > 5) {
    $rounded = (1+intval($tmp/10))/100;
} else {
    $rounded = intval($tmp/10)/100;
}
echo $rounded,"n";

$ php -r 'printf("%.40fn", 13.775);'
13.7750000000000003552713678800500929355621

$ php -r 'echo round(13.77500000000001, 2, PHP_ROUND_HALF_DOWN) . "n";'
13.77

function round_half_down ( $num, $digits ) {
    $mul = pow( 10, $digits );
    return ceil( $num * $mul - 0.5 ) / $mul;
}