<?php

function round_to($number, $increments) {
$increments = 1 / $increments;
return (round($number * $increments) / $increments);
}

function ceil_to($number, $increments) {
$increments = 1 / $increments;
return (ceil($number * $increments) / $increments);
}

function floor_to($number, $increments) {
$increments = 1 / $increments;
return (floor($number * $increments) / $increments);
}


$n = 11.86756756;
$i = 0.5;

echo ceil_to($n, 0.5);  // 12
echo "\n";
echo floor_to($n, 0.5); // 11.5
echo "\n";
echo round_to($n, 0.5); // 12