While at BYU I worked as a waiter in Provo and each night I had to report how much I made in tips. I would average about 10% in tips compared to my total sales. I worked there for two years. I moved to Dallas to go to grad school and transferred for a few months to another restaurant (same franchise) before school started. I did nothing different and regularly averaged 20% in tips compared to total sales. Mormons in general tip less or at least have not been educated in tipping etiquette.
So yes, by my highly strict standards of experimentation and observation Mormons are cheaper than most other sub sets of the population. the church is still true though...