Interest and penalties for late estate tax payments

(a) Any tax due under this chapter that is not paid by the time prescribed for the filing of the return as provided in section 236E-9, not including any extension with respect to the filing of the report or the payment of the tax, shall bear interest at the rate in section 231-39(b)(4) from the date any tax is due until paid. (b) If the return provided for in section 236E-9 is not filed within the time period specified, unless it is shown that the failure to file is due to a reasonable cause, then there shall be paid, in addition to the interest provided in this section, a penalty equal to five per cent of the tax due in respect to the transfer, or five per cent of the additional tax due in the case of a supplemental return, for each month beyond the time periods that the return has not been filed; provided that no penalty so imposed shall exceed a total of twenty-five per cent of the tax. (c) If the Internal Revenue Service waives the penalty provided in the Internal Revenue Code for failure to timely file the federal return or the penalty for failure to timely pay the federal transfer tax liability, the waiver shall be deemed to constitute reasonable cause for the purposes of this section.