State Tax minimums VA, ME, TN, NH

I have earned income as a contract worker in states I am not a resident of - VA, ME, TN, and NH.  In each state, it's not been a lot of income in that state. I don't want to file in a state I do not have to; however, determining the amount of each of these states is not straight-forward that I can find. What are the minimum requirements for contract work in each of these states?