In Europe, prices have to already include VAT: the digital list price (DLP) you set is the final price readers pay. There is no extra VAT or other tax added. VAT will be withheld by the stores automatically.
From 2015, the applicable VAT rates are based on the country where the buyer is resident within the EU. Thus, when a German reader buys a book, 19% VAT will be deducted, while if a Hungarian one, 27%. In some countries, there is no VAT on ebooks.
In the USA, sales tax differs by the state.