Anyone know of a way to apply Canadian Harmonized Tax or on top method in 11i?

I need to create a tax group that will perform the following. For an item i need to apply tax then once that is calculated i need to apply tax on top of the combined amount. For example, i receive an invoice for 100.00 and need to apply GST at 5%, which equals to 5.00. The total tax and item amount will be 105.00. now i need to apply the other tax amount, let's say PST at 7% to the 105.00, which equals to 112.35. (100 x 5% = 5.00; 105.00 x 7% = 7.35; total inv amt is 112.35)