There is a product, available in head shops and online called Quick Fix 4.0. It is synthetic urine, sold in a small 2oz bottle. It is absolutely identical in all ways to clean urine, and the labs cannot detect it. You heat it in the microwave to 100 degrees, using the temperature strip on the outside of the bottle. Then, you place the bottle in a place that will keep it near that temperature - your crotch. (If the urine you give them isn't near body temperature, they know you cheated) You go take the test, pour the bottle into the sample cup and ALSO pee (for real) in the toilet. You will DEFINITELY pass as long as the temperature is correct.
They also sell pills and drinks that supposedly work, but they don't.
Before you flame me, I don't think working a record store requires drug testing, and is an invasion of privacy. As long as you are achieving or exceeding expectations, it's none of their business if you like smoking a joint on your time off. It's not like you'll be carrying a gun or peoples lives will be at stake because you got high the night before. I'm a firm believer that as long as it's done on your own time, what you do is none of your employers business.
Getting high on the job though, thats another story. I don't do it, and have had people fired for doing exactly that.