There are 3 types of invoices in RISE.  

1. Taxable
2. Non-taxable 
3. Mix (Taxable and Non-taxable)

In the invoice add/edit modal, you can select the tax percentage. The tax percentage will be only applicable for the items which are taxable. If you don't mark any item as taxable, the tax percentage will not be applied to the item.

Please check this video to learn more: