<?php
$allowed = array (15, 28); // List here all the non % 10 value you want to print
for($i=10; $i<=50; $i++) {
    if ($i % 10 === 0) {
        echo $i."\n";
    }
    else if (in_array($i, $allowed)) {
        echo $i."\n";
    }
}
?>

10
15
20
28
30
40
50