The example listed on the number_format page is not taking into account the rounding of the value returned.

http://www.php.net/manual/en/function.number-format.php

<?php

    $number = 1234.56;

    // english notation (default)
    $english_format_number = number_format($number);
    // 1,234.56

    // French notation
    $nombre_format_francais = number_format($number, 2, ',', ' ');
    // 1 234,56

    $number = 1234.5678;

    // english notation without thousands seperator
    $english_format_number = number_format($number, 2, '.', '');
    // 1234.56

?>

The last output should be 1234.57