Cash? Those bills have serial numbers on them! I'm not sure exactly how frequently they're checked or scanned by banks, but a scanner in the ATM you withdrew

Cash? Those bills have serial numbers on them! I'm not sure exactly how frequently they're checked or scanned by banks, but a scanner in the ATM you withdrew from + scanning the daily deposits by the gas station would paint a pretty clear map, even if a few of them get tendered back out as change, and a few more aren't tracked due to OCR failures. Best stick to bills tendered as change only. Although who knows what red flags someone trying to hide their spending habits might be able to trip, alerting the feds that someone frequenting your favorite restaurant is trying to hide their trail...