You may not be able to find out online. It depends on the town tax office ... if they are online ... you can get it.
Probably the best (and easiest) is to call the tax office in the town of your prospective house. Ask for the total true taxes both town and county as well as school and they'll be able to get those for you.
If this is going to be your promary residence ... you may qualify for the STAR rebate and you can ask them that amount at the same time.