To define tax rates and exemption profiles, go to back office Settings > Taxes.
Create a tax rate
To create a tax rate tap 
Add and give the tax rate a name, if it's the default rate, the percentage and tax code then tap 
Save.
On the tax list page, the table displaying the different tax rates, display a number on each line. This number represents the number of products assigned with that tax rate. If no products are applied, you'll see a bin icon giving you the option to delete the rate.
Click a tax rate to edit or delete it.
Apply a tax rate to a product
Tax rates can then be specified from the Details tab when adding/editing a product. The default tax rate is applied to the product which is editable from the dropdown list.
If using the bulk csv import or editing existing products in bulk via csv, use the TaxCode column using the tax code created in the back office. The tax code must first exist in the back office before importing.
Create a tax exemption profile
To create a tax exemption profile tap Add and give the exemption a name, whether a signature is required to use the exemption and the product categories that apply to the tax exemption being created. Once complete, tap Save.
Apply a tax exemption profile to a customer
Please refer to the tax exemption on how to apply exemptions and how to use them on the POS.