I'm not sure what to tell you, except why look the gift horse in the mouth? If your cart will take both a minimum quantity and a "increment" number, I'd use it ... consider the well known mantra "don't reinvent the wheel", or the OS Holy Wars axiom: "Instead of asking why a piece of software is using '1970s technology,' start asking why software is ignoring 30 years of accumulated wisdom."
With PHP, you've got [man]round/man and [man]ceil/man, but even round() with a precision of -2 is going to ... round it off. So:
$quan_entered=101;
echo round($quan_entered,-2); // prints 100
$quan_entered=151;
echo round($quan_entered,-2); // prints 200
The solution, then, if you really wanted to do this, would be to write your own function which accepted the increment quantity (which is the same as the minimum, if I understand correctly) and returned the next increment for any value above an increment ... so there's little difference except you already have code that basically does just that.
You can, obviously, roll your own. Here's a hint:
<?php
$it="widgets";
$wanted=209;
$increment=100;
if ($mod=$wanted%$increment) { // they want more than the minimum
$number_ordered=$wanted-$mod+$increment;
}
echo "You wanted $wanted $it, but we'll have to send you $number_ordered $it \n";
?>
I think you'd not only have the functionality already written, but it would be more "up front" for your site visitors, if the drop down box had the quantities they could order, just as you state.
