Shauk,
I would be working my ass off to find another job. It's good to work in a situation like that so you know what its like, but its enough to know you don't want to do it for too long. That sounds like a rip that they dont pay for the use of your own car; I would definately find another place of employment.
I usually tip pretty well. The web site
http://www.stainedapron.com/ will have some funny stories for you if you work in the waiting or even the pizza delivering industry. They have some funny stories on there, also it makes you not want to rip off your waiter/delivery guy.