316 Neb. Admin. Code, ch. 23, § 012
Any person subject to tax under the Nebraska Revenue Act of 1967, as amended, or any person required to file an information return for the taxable year, shall keep such permanent books of account or records, including inventories and all supporting documents, as are sufficient to establish the amount of gross income, deductions, credits, or other matters which may be required to support any income tax or information return.
Such books or records shall be kept available at all times for inspection by the Tax Commissioner or any agent or representative designated by him for the purpose of ascertaining the correctness of any return or other document required to be filed under the Nebraska Revenue Act.
Each taxpayer shall retain all of his records relating to a taxable year as long as their contents may become material in the administration of any Nebraska tax laws. If the Tax Commissioner serves a notice of deficiency for a taxable year, the taxpayer shall retain all of his records relating to that taxable year until the deficiency has been satisfied, abated, settled, or disallowed.
316 Neb. Admin. Code, ch. 23, § 012