Shopping Card Update

I need to update a shopping card to add a new tax and shipping rate. These are not firm requirements, I've looked at the code and it seems like the easiest way to do it. Once you see the code you can suggest alternate options. 1) Add, HST (cost * 0.13) for digital purchases, these product fields begin with letter D. The cart already charges GST (cost * 0.05) for all products, I would like to add HST for digital purchases. 2) Shipping for digital purchases should be $0, and remain the same of existing products. 3) Add a GST and HST field for all purchases.