There's no penalty to filing a 1040X..But you need to do it. In TTAX you enter your current year state and local taxes withheld in the W-2 window. Then you go to another window called Tax payments(or somehting like that). There you enter your estimated taxes (for those that do) and down the bottom is a place to enter state and local taxes paid for prior years. Your current year withholding state taxes and prior year taxes paid get combined and transferred to the state taxes line of schedule A. If you didn't enter those taxes paid for a prior year you should file an amendment and get a refund.

Joe Varga