Tip is of no concern here. It's a gratuity that may be given, outside the check, to the server.
The tax rates have to be declared on the product label. VAT is 23%, 13% or 6%, depending on the nature of the product. Basic food items and basic necessities, like baby diapers, are 6%. 13% is usually reserved fro restaurants and everything else goes into the higher rate.
Fuels, tobacco and so called luxury items have other taxes added to it, which are declared in the receipt.
It isn't an opaque practice.