Surcharges: ability to select only the applicable tax rate for each surcharge (e.g. GST only not GST/PST)

We need to use two different tax rates here in BC:

1. GST (5%) - applicable on all property rental fees and surcharges
2. PST (8% for us) - applicable on Property Rental Fee only.

Right now we are manually correcting the tax amount by removing the % and manually entering a tax amount. This is liable to human error & a legal issue if we make a mistake.

Can you develop a way to select which taxes apply to which surcharges?