Within thirty days of the receipt of a claim for a refund of tax, the commissioner shall examine the claim and, if there are no apparent discrepancies, shall prepare an abstract showing the claim number and the name, address, and the amount due each claimant. All claims approved by the commissioner must be paid by warrant-checks prepared by the office of management and budget. The state treasurer is not required to retain the canceled checks by which any refund may have been paid for a period of more than six years from July first of the fiscal year in which the refund check is issued.