File tax returns in your home state (IA) and in any state where you physically worked (TN). Do not file a NE tax return.
It is irrelevant where your employer was located - you only owe tax to your state of residence and any state where you earned money.
Your home state (IA) taxes all your income, wherever it is earned. Other states can only tax income you earned in their state. IA will give you a tax credit for the TN taxes (nonresident state) you paid on your IA tax return (resident state). This is how the states avoid double taxation, by allowing a state credit in your home state.
Just follow the TurboTax guide when working on your states (remembering to do your non-resident state return first) and TurboTax will do all the calculations for the credit to your resident states return
