(35 ILCS 120/7) (from Ch. 120, par. 446)
    Sec. 7. Every person engaged in the business of selling tangible personal property at retail in this State shall keep records and books of all sales of tangible personal property, together with invoices, bills of lading, sales records, copies of bills of sale, inventories prepared as of December 31 of each year or otherwise annually as has been the custom in the specific trade and other pertinent papers and documents. Every person who is engaged in the business of selling tangible personal property at retail in this State and who, in connection with such business, also engages in other activities (including, but not limited to, engaging in a service occupation) shall keep such additional records and books of all such activities as will accurately reflect the character and scope of such activities and the amount of receipts realized therefrom. The Department may adopt rules that establish requirements, including record forms and formats, for records required to be kept and maintained by taxpayers. For purposes of this Section, "records" means all data maintained by the taxpayer, including data on paper, microfilm, microfiche or any type of machine-sensible data compilation.
    All books and records and other papers and documents which are required by this Act to be kept shall be kept in the English language and shall, at all times during business hours of the day, be subject to inspection by the Department or its duly authorized agents and employees.
    To support deductions made on the tax return form, or authorized under this Act, on account of receipts from isolated or occasional sales of tangible personal property, on account of receipts from sales of tangible personal property for resale, on account of receipts from sales to governmental bodies or other exempted types of purchasers, on account of receipts from sales of tangible personal property in interstate commerce, and on account of receipts from any other kind of transaction that is not taxable under this Act, entries in any books, records or other pertinent papers or documents of the taxpayer in relation thereto shall be in detail sufficient to show the name and address of the taxpayer's customer in each such transaction, the character of every such transaction, the date of every such transaction, the amount of receipts realized from every such transaction and such other information as may be necessary to establish the non-taxable character of such transaction under this Act.
    Except in the case of a sale to a purchaser who will always resell and deliver the property to his customers outside Illinois, anyone claiming that he has made a nontaxable sale for resale in some form as tangible personal property shall also keep a record of the purchaser's registration number or resale number with the Department.
    It shall be presumed that all sales of tangible personal property are subject to tax under this Act until the contrary is established, and the burden of proving that a transaction is not taxable hereunder shall be upon the person who would be required to remit the tax to the Department if such transaction is taxable. In the course of any audit or investigation or hearing by the Department with reference to a given taxpayer, if the Department finds that the taxpayer lacks documentary evidence needed to support the taxpayer's claim to exemption from tax hereunder, the Department is authorized to notify the taxpayer in writing to produce such evidence, and the taxpayer shall have 60 days subject to the right in the Department to extend this period either on request for good cause shown or on its own motion from the date when such notice is sent to the taxpayer by certified or registered mail (or delivered to the taxpayer if the notice is served personally) in which to obtain and produce such evidence for the Department's inspection, failing which the matter shall be closed, and the transaction shall be conclusively presumed to be taxable hereunder.
    Books and records and other papers reflecting gross receipts received during any period with respect to which the Department is authorized to issue notices of tax liability as provided by Sections 4 and 5 of this Act shall be preserved until the expiration of such period unless the Department, in writing, shall authorize their destruction or disposal prior to such expiration.
(Source: P.A. 88-480.)