Most pizza places now charge a $3-5 delivery fee. That is the tip!
I live in a city and surrounding cities where sales tax runs 7.75 to 8.75%. So for a sit down meal I tip 2x the sales tax amount, no calculator needed. A little more or less depending on the quality of service. For to go orders from Restaurants that typically are sit down eateries like a Chili’s, Olive Garden and what not I typically give a flat $3 which works out to about 7-8% of the bill.