The Division of Taxation is authorized to enter into a written agreement with any taxpayer relating to the liability of such taxpayer in respect of any tax, fee, penalty or interest heretofore or hereafter imposed by this act, if it is found that such agreement is in the best interests of the State, which agreement shall be final and conclusive, and except upon a showing of fraud, malfeasance, or misrepresentation of a material fact:
(a) the case shall not be reopened as to the matters agreed upon or the agreement modified, by any officer, employee, or agent of this State, and
(b) in any suit, action, or proceeding, such agreement, or any determination, assessment, collection, payment, cancellation, refund or credit made in accordance therewith, shall not be annulled, modified, set aside or disregarded.