You can always call the police to come to the scene and make an accident report. This may deter him from future incidents. He could be cited for failure to keep a proper lookout and failure to control speed (amongst others). Also, if he is constantly hitting your car, he may be doing it intentionally or he may be under the influence of alcohol or drugs.
In short, you do not need major damages to call the police and you should report this the next time it happens and tell the officer of the previous incidents. It can't hurt to make the report, and may deter him from hitting your car. Also, many other things besides a citation may happen. For example, he may not have proof of insurance, inspection, registration, or a valid driver's license; may be under the influence of alcohol or drugs; and may even have outstanding warrants. This may result in multiple citations or even his arrest.