He is the boss and pays you for your time. How he chooses to spend that time is up to him. As long as he isn't asking you to do anything that is illegal, or morally repugnant, do it.
That is what you are getting paid for.
The long winded explanation:
When you start working for someone or a company, there is at least an implied contract of work for hire (US specific, probably applicable elsewhere). This means that you the employee get compensated (paid with money, services, or goods) for performing some service. Anything you produce as a part of the work for hire is a product owned by the person or company that retained you, once you have been compensated.
You are obligated legally to not perform any action that would be illegal in your area. You can refuse to perform any service or task that is illegal. Doing so may cost you your job. There are legal protections in place to prevent that (again it highly depends on your area).
As for things that are morally repugnant, most reasonable people will never ask you to cross that line. If your boss knows that you are a vegan, but requires you to prepare meats for eating, that may cross the line for you. You can refuse to perform that service. It may cost you your job, probably not though. There may or may not be legal protections in place to prevent the loss of your job on these grounds.
With anything that involves the law, you should seek the advice of a lawyer in your area.