Simply add the name of the tax and the rate on your Ticket settings page and then choose for which of your ticket type you want the tax to be added to. The tax is then automatically added to the ticket price that you have set.
I am from the EU and worried about tax calculations!
We feel you! So, we have built the system based on the latest EU regulation, including the rules of 'reverse charge'. If you are in an EU country and you add tax to a ticket, it will be deducted from the price automatically when it's relevant. The deduction is based on the country of the ticket buyer and whether s/he's acting as a private person or representing a company.