You can claim Sales Tax in the Deductions & Credits section. You can also add it to the basis of the new vehicle.
If you had been claiming Vehicle Expenses in the Rental Expenses section, you are correct that you can indicate your stopped using the vehicle (and date) and any miles in 2017 for a 2017 mileage deduction.
'Traded it in' refers to replacing a business vehicle with another one, and is considered a 1031 exchange, which defers any gain for depreciation recapture of the old vehicle.
Type 'like kind' in the Search window, and 'Jump to like kind' to report the exchange of old/new vehicles. TurboTax will calculate a 'basis' for the new vehicle, which you can enter in the Rental Expenses section.
Here's more info:
https://ttlc.intuit.com/replies/3301982
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