On my 1099-DIV there is no state listed in box 13, but TurboTax will not allow me to leave the state selection blank.

Enter the abbreviation for your state of residence in box 13 and 0.00 in box 15.  You can leave box 14 blank.

If you did not have any state taxes withheld directly from the invested company, return to the "Tell us if any of these uncommon situations apply to you" screen and ensure that the "State taxes were withheld..." check box is clear (not checked). Then proceed to the next prompted question. If box 13 is blank on your 1099-DIV, it should mean that no taxes were withheld, and your 1099-DIV should not have any entries in boxes 13-15.

I hope this helps!

Click on "I earned exempt-interest dividends in only one state".  In the pull-down list for the State box, go all the way to the end of the list and select "Multiple States".