When you are entering information from your W-2, DD is an option. DD is the code for the cost of employer-sponsored health coverage.
Next, you note that your home state of Tennessee isn't listed in Box 15. This is because Tennessee does not have an income tax. There's nothing you need to report in boxes 15 through 17. If you had income tax withheld from another state, you would report it here, and indicate the state that withheld the tax, not Tennessee.
