N.J. Stat. Ann. § 54:18A-1.1

The director may for reasonable cause extend the time, not to exceed 30 days, for filing any return under the rules and regulations as he shall prescribe, which rules and regulations may require the filing of a tentative return and the payment of an estimated tax to the director. If the time for filing the return shall be extended, the payment of the portion of the tax remaining to be paid, if any, shall be postponed to the date fixed by the extension of the time for the filing of the return, but in every case the corporation shall pay, in addition to the unpaid portion of the tax, interest thereon at the rate as provided in the state tax uniform procedure law, subtitle 9 of Title 54 of the Revised Statutes, from the time when the return originally was required to be filed to the date of actual payment under the extension; provided, that if the unpaid portion of the tax is not paid within the time fixed under the extension, the interest on the unpaid portion shall be computed at the rate as provided in the state tax uniform procedure law, subtitle 9 of Title 54 of the Revised Statutes, from the date of the tax was originally due to the date of actual payment.