What must cashiers use to correct an error in a sale?

The correct answer is AF Form 645, Cash Register Adjustment, because this specific form is designed for recording adjustments made to transactions within the cash register system. It allows cashiers to document errors accurately and maintain the integrity of financial records. Using the AF Form 645 ensures that any corrections are officially noted and properly accounted for, which is crucial for financial accuracy and accountability.

Other options do not serve the same purpose. For example, while a transaction receipt provides a record of the sale, it does not facilitate correction of errors. Manual adjustment forms and cash management forms have their own specific uses but are not tailored for correcting sales errors in the same way that the AF Form 645 is. By using the appropriate form for adjustments, cashiers enhance the reliability of transaction records within the USAF Services operations.