If you get a certain amount of fuel at most truckstops say 50 to 100 gallons you get one for free if not it will range between $5 and $10
Even if you take your shower on your freebie card from the various truckstops, it is common courtesy to leave a tip for the guy who cleans the shower room. I typically leave 2 dollars on the sink for him as I leave. And if the shower was clean and ready to go, I tell him "thank you" as I go out if I see him.
I'm just hoping my Mentor, who I will share a truck with for 42 days, is as hygiene conscious as I am... Please, Please, Please...