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.
Another major difference is that in most countries the VAT is already added to the price of the book in the store and the buyer sees this before purchasing, while in the US the VAT only gets added at the checkout.