What do I do about my roommate's lying?

I've caught him in several lies over dumb stuff, like adolescent drug use, that something was a gift his mom found at Goodwill vs. he bought it cheap from Target, he paid the rent check last week vs. he just sent it yesterday, he quit smoking with no help vs. he used the patch to help him quit, etc. A lot of times he tells me things, forgets he told me, and then tells me a different version later. The problem is that it's undermining my trust of him in general. For example, I was missing some money which I could have lost or spent myself and forgot, but I started suspecting him of stealing it. I've tried telling him in a joking, laughing way that I know better when he changes his story b/c he had already told me differently earlier , just to get the point across that I know he's bullshitting me without being confrontational. It's a touchy situation b/c the lease is in his name and if I say, "Dude, quit lying. I can't trust you," he could throw me out on my ***, and I'd be screwed