We at osCommerce are witnessing rounding problems in our 
taxes logic and have made a reproduceable script below. 
 
number_format() produces different rounding results when 
floats or strings are passed to the function. 
 
<?php 
  $price = '100.0000'; 
 
// Canada GST 7% 
  $price = '1.07' * $price; 
 
// Canada/Quebec PST 7.5% 
  $price = '1.075' * $price; 
 
  echo '$price: ' . $price . '<br>' . "\n" . 
       'number_format($price, 2): ' . 
number_format($price, 2) . '<br>' . "\n" . 
       'number_format((string)$price, 2): ' . 
number_format((string)$price, 2); 
?> 
 
The correct results are produced when the string value is 
passed. The float value produces incorrect results. 
 
I do not know if this is a problem with the number_format 
function, or if it is due to floats/mathematics. 

It's a float/maths problem, nothing to do with PHP specific.

Derick

The script:

<?php
      echo number_format(63.745, 2, '.', "") ."<br>";
      echo number_format(64.745, 2, '.', "") ."<br>";
?>

Result:

63.74
64.75