Отбросить дробную часть числа без округления

toFixed.php

<?php

function toFixed($number, $fix = 2) {
    $arr = explode('.', $number);
    return isset($arr[1]) ? floatval($arr[0] . "." . substr($arr[1], 0, $fix)) : $number;
}

// Test
foreach ([
    1 => 1.123456,
    2 => 2.12345,
    3 => 2.562355,
    4 => 40.1134,
] as $fix => $number) {
    echo "number=" . $number . ", fix=" . $fix . " => " . toFixed($number, $fix) . "\n";
}

Результат:

number=1.123456, fix=1 => 1.1
number=2.12345, fix=2 => 2.12
number=2.562355, fix=3 => 2.562
number=40.1134, fix=4 => 40.1134