The common stock of Quality Systems Inc. began trading Monday on the Nasdaq over-the-counter market system. And although the overall market remained in the grip of a losing streak, dropping 42.61 points for the day, Quality System's common stock rose 50 cents to close at $6.50 a share in light trading. The Tustin company develops and markets automated management systems for medical and dental group practices. It has clients in 45 states, Canada and Saudi Arabia. The stock previously traded in the so-called Small Cap market, which specializes in smaller companies.