I rarely have this conundrum but like most answers to life’s questions, I’d say the answer is “It depends.”
If it’s a high-end, established taxidermist doing a shoulder mount that will take 12-18 months to complete and you’re paying top dollar, I’d say probably not. You’d “tip” that taxidermist just by being a good, patient, cash-paying client. No need to start calling after the first month and every month thereafter to “check on the progress” then whip out a credit card and ask for a receipt when it’s time to settle up.
But if the taxidermist drives from Young and meets you in Payson so you can pick up a skull cap mount, an extra $20 for his gas would be appropriate, even if he had to go to Payson anyway. (But even then, it would probably surprise the taxidermist.)
If it’s a young person who’s in school, on the football team and student council and cleans/bleaches skulls for a side hustle, I’d hand over more cash than required and say “I appreciate your hard work. I don’t need any change back.”
So it depends, I guess.