Retail sales Tax Sales taxes generally take one of two forms A unit tax is a given amount for each unit purchased (e.g, motor fuel tax that is a certain number of cents per gallon of gasoline An ad valorem tax is computed as a percentage of the value of the purchase6 Retail Sales Tax • Sales taxes generally take one of two forms: – A unit tax is a given amount for each unit purchased (e.g., motor fuel tax that is a certain number of cents per gallon of gasoline). – An ad valorem tax is computed as a percentage of the value of the purchase