Problem with checkout math (Coupon and Tax related)

[onLoad]

For some reason when I add a free shipping coupon, the math goes weird at checkout.

Sub-Total: $120.00 United States Postal Service (1 x 3.509lbs) (PARCEL): $12.45 Tax: $10.50 Discount Coupons:SHIP08: -$12.45 Total: $129.41
Free shipping is for orders over $75, and tax is 8.75%. Any know where I can find the area where this is calculated? Or any ideas on what might cause this?

[michael_s]

The problem is that your tax is on the 120+$12.45= $11.59 which equals the $1.09 miscalculation that you are seeing, even though the tax amount says $10.50. Check the shipping and tax settings to make sure neither are set to tax the shipping.

Have you changed the sort order of the Order Total modules? That is usually the cause of these types of problems too.

[onLoad]

Thank you, I don't remember changing the any files in that area, but I have found the problem. In my version of ot_coupon.php there is this line:

//New code for tax recalculation fix
if ($tod_amount == 0 || $tod_amount == '') {
$pct = $order->info['tax'] / $order->info['subtotal'];
$order->info['tax'] = $order->info['tax'] - ($pct * $od_amount);
foreach ($order->info['tax_groups'] as $key => $value) {
$value = $value - ($pct * $od_amount);
$order->info['tax_groups'][$key] = $value;
$order->info['total'] -= ($pct * $od_amount);
}
}
//end new code

I removed that and now it calculates everything correctly. I had a feeling there was a problem with it re calculating tax after the discount, but I was unsure where that would be.

Thank you for the quick reply too (although now that you mention it, where is the setting to set tax onto shipping?