Interest on underpayments of tax shall be due and payable at the rate of ten percent (10%) per annum from the date such tax was due to be paid until the date of payment. Sales and use tax is due to be paid on the twentieth (20th) day of the month following the month in which the sale occurs. Interest on any unpaid sales or use tax begins to accrue on the twenty-first (21st) day of the month in which the tax is due.