In some jurisdictions, the car tax on motor vehicles (cars, trucks, motorcycles, and vans) is prorated to reflect the time the vehicle was normally garaged in the jurisdiction, but in others, the property is assessed and tax determined as of January 1 of each year.
If you have sold a vehicle or moved the vehicle out of the locality, you need to notify the assessing official (often the Commissioner of Revenue) so that the vehicle can be properly removed from the tax rolls.