Some resources may be combined with the County's down payment assistance program. This form certifies the purchase price and determines the sales tax you must pay when registering the vehicle.How much of a down payment is required? The bill of sale must show the purchase price and the amount of out-of-state sales tax paid to the dealer. Providing downpayment and closing cost assistance for first-time homebuyers through the HOME Downpayment and Closing Cost Assistance Program.