In a graduate school international business accounting class I was taught that, in Europe (and most of the rest of the world), the word "turnover" is the same is "sales." So on a European income statement, the top line is "Turnover." Not "Sales," as in the USA.

So a "turnover tax" is the same as a "sales tax."

"Service charge" or "Service fee" is a gratuity. Turnover tax is tax.