DETROIT — If you’re in the market for a Japanese car, March is a good time to buy. Unlike U.S., European and Korean automakers, which end their financial year on Dec. 31, Japanese companies such as Toyota Motor Corp. and Honda Motor Co. close their books on March 31. In order to hit their annual sales targets, Japanese automakers usually ramp up the promotions and deals in March. Honda’s “Dream Garage” ads are currently running between college basketball games.