Does the word 'tithe' have a family?

Most restaurants these days supply patrons with a tipping guide printed on the check, often with a range of suggested gratuities for service well beyond the call of duty. Anticipating that churches might also board this bandwagon with suggestions for pledges of more than 10%, I was wondering if there are words akin to the term ‘tithe’ for, say 15%, 18%, 20% and even 30% (as is laughingly suggested as a tip for truly outstanding service at my local Italian restaurant)? Anyone know?