Tax After Discount
I want to add 10% GST tax to the sub total of the cart after discount. I used the charges tab of the eCart object and set it up to the cart subtotal * 0.1 and checked the "apply after Discounts" checkbox (see gst_1.gif). The calculations are all wrong on the confirm.php page (see gst_2.jpg). The GST charge in this example should be $72.73 - $18.18 * 0.1 which should equal $5.45. I thought that it may have been including the shipping in the calculation (that would have been $6.82 if it was) but I have the checkbox "Include in cart subtotal when calculating sales tax" deselected.
One thing I did notice is that the "apply after Discounts" checkbox on the eCart objects Charges tab doesn't save, that is if you go back into that tab again, you have to select the checkbox again.