I generally tip the pizza delivery person $2 for the first pizza and add a dollar for every additional pizza. Never 15 or 20 percent like in a restaurant.
Another tipping options has happened in the past few years. At smaller stores pizza place, doughnut shops, etc. leave a jar on the counter with a sign taped on it "Tips". I rarely put anything in it as I should tip a cashier for doing their job? Does Russia, Ukraine, Belarus etc. have such a thing?
Scott