You can find this page in the Shop settings menu. When you create your shop we automatically set that all your prices are with included taxes. If that is not true you can unmark the checkbox and set taxes for countries you are selling in. Here you see all the countries that you’ve added in the Shipping section. They are grouped as you’ve added them to shipping zones. To set tax for a country just click on it. On the page that will open write the tax and if it’s the same for all regions apply it with the button. Taxes are in percentage.

Here you also add tax for your POS devices if you use such. It’s automatically set to 25% but you can change that, too.