Never burn bridges when it comes to jobs and business associates if you can help it. The guy may be on a power trip, but if you can endure it until you find a better job, do it.
You could be the professional one and go to him and discuss in person the situation. Keep anger and accusations in check even if he loses it. Inform him that you were not aware that these new chores were in your job description but that you'd be willing to do your share along with everyone else(or if it's to be your assignment alone, discuss what concessions are to be made elsewhere). He is the boss or owner, it's his company and his peroragative to have his employees do whatever he wants as long as it's not illegal(unless you have a contract stating otherwise). I worked for a man once, who would have you go to his house and mow his yard, work in his garden, make deliveries for his other businesses and sweep the floor if it needed it. It all paid the same, even though I wasn't doing what I was hired to do.