Iowa Admin. Code r. 701-20.11
Retailers are required to keep records of and report the actual total gross sales for each filing or reporting period. A deduction may be taken for all tax-exempt sales but a record must be kept to substantiate all deductions taken.
Certain retailers finding it difficult to maintain detailed records of their taxable and nontaxable retail sales may alleviate this difficulty by the use of a formula method which will reasonably approximate the actual taxable receipts.
Written approval must be obtained from the audit and compliance division of the department to use a formula method. If a retailer requests an alternate formula, the retailer shall first list the reasons why an alternate formula is necessary and, secondly, shall outline the proposed formula in detail. If approval is given, the department reserves the right to withdraw or require an update in procedure at any time.
The use of the formula is an authorization for reporting the most accurate amount of taxable and nontaxable gross receipts but the retailer shall be responsible for the actual tax liability. Additional assessments may be made if an audit discloses the formula is not producing the proper tax payments.
Iowa Admin. Code r. 701-20.11