State tax filing

What you are calling a penalty is actually interest on the underpayment. TurboTax asked you whether you wanted to have the state Division of Taxation calculate the interest. You must have chosen that option.

The screen that asks that question is confusing. You have to read it very carefully. It doesn't ask you if you want TurboTax to calculate the interest. It asks if you want to have the state calculate the interest or if you want to "see if you can reduce the interest." If you click the "Calculate" button you are choosing to have the state, not TurboTax, calculate the interest. If you want TurboTax to calculate it, you have to click "Reduce Interest," and then answer the follow-up questions. The screen might subtly nudge you towards having the state calculate it by telling you that "If you choose Calculate, you don't have to provide any other information."