Unless a different period of time is prescribed by statute, for each electronic return of taxes, fees, interest, penalties or other charges, the taxpayer shall keep records, receipts, invoices and other pertinent papers to substantiate the electronic return for 4 years following the later of the due date of the return or the date the electronic return was filed with the Department.
Nev. Admin. Code § 360.598
NRS 360.090, 360.092