Yeah, I don't believe that for a minute. If "the grid" (meaning oh-so-much more than the power grid) goes down, currency fails in a fairly predictable order: checks, credit cards, debit cards, and then paper money over a VERY short period of time. Read up on Argentina's economic collapse circa 2001. Nobody would take plastic of any kind, because of limits on bank withdrawals. Even for businesses. So if you take in digits, and can't spend them to replenish stock, you are no longer a business. It was cash, preferably foreign cash, and gold or silver that ruled the day. People started keeping scales and cutters to snip off links of 24k gold chains for payment.
Bullion and specie maintains value and increases in fluidity even during a big emergency. Paper currency gets sneered at.
And so every single transaction can be tracked electronically. Just as FDR outlawed possession of gold coins or indeed any gold bullion other than what is contained in wearable jewelry, to prevent people from avoiding government manipulation of the currency and economy. If he'd had the technological ability to outlaw cash transactions like we do now, you can bet your ass he would've tried.