To apply two separate tax rates on the same product (or service), you must first create a new tax that will include the two tax rates you wish to use.
When creating a new tax in Nutcache, you can add several components that are actually independent, unless you check the "Compound" option. For example, you can create a "My Area Taxes" including a GST (5%) and a PST (9,975%) component so that when you apply this "My Area Taxes" to items in your invoices or estimates, the two components will appear separately with the proper amount displayed for each of them.
How to set up a compound tax?
A compound tax is a tax calculated on top of a primary tax. So to create a compound tax, add two components to your tax where the second one is calculated on top of the first one as shown below: