Time taxes due — Interest and additions to tax on delinquent payments

All taxes imposed by chapter 22 of this title, unless provided, are due and payable nine (9) months after the date of death of the decedent. If the taxes are not paid within nine (9) months from the date of death, interest shall be charged and collected at the annual rate provided by § 44-1-7 from the time the tax is due, determined without regard to any extension of time for payment. In addition, if the taxes are not paid when due (determined with regard to any extension of time for payment), there is added to the amount of tax due five-tenths percent (0.5%) of the tax per month to a maximum of twenty-five percent (25%) unless it is shown that the failure to pay is due to reasonable cause and not due to willful neglect.