(1) The Tax Commissioner, or any person authorized in writing by him, is authorized to enter into an agreement with any person relating to the liability of such person, or of the person or estate for whom he acts, in respect to the tax imposed by the provisions of the Nebraska Revenue Act of 1967 for any taxable period.

(2) Such 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 matters agreed upon or the agreement modified by any officer, employee or agent of this state; and

(b) In any suit, action or proceeding under such agreement, or any determination, assessment, collection, payment, abatement, refund, or credit made in accordance therewith, shall not be annulled, modified, set aside or disregarded.