Function Bulatkan Angka (Dinamis)

<?php
function bulatkan_angka($ke, $num) {
    $potong1 = substr($num, 0, $ke-1);
    $potong2 = ceil(substr($num, $ke-1, strlen($num)));
    $bulat = substr($potong2, 1, 1);
    $bulat1 = substr($potong2, 0, 1);
    $bulat2 = $bulat>=5?$bulat1+1:$bulat1;
    $nol = "";
    for ($i = 0;$i < strlen($potong2)-1;$i++) {
        $nol .= "0";
    }
    $hasil = $potong1.$bulat2.$nol;
    echo (int)$hasil;
}

bulatkan_angka(4, 8161824.6);
?>