Example, as a teenager mowing lawns for your neighbors, you just told the IRS you made $x,xxx mowing lawns for the fiscal year. Not that your neighbor named Susan at 1234 fake street paid you $xxx/month to mow her lawn 4 times a month, or that Joe from 4321 real street purchased the upcharged package that includes managing his compost bin.
Cash is the undisputed champion of privacy for financial transactions.
I can use cash to buy groceries or a soda at the corner store each day, and while I suppose I'm not entirely anonymous to those parties I may as well be. The grocery store is certainly reporting my cash transaction to the appropriate authorities.
Sure, this doesn't apply for all use cases. However, it applies for a lot of things that currently are tracked by using electronic forms of payment. These spending patterns were simply not tracked on an individual basis until the advent of the shopping club cards, which eventually became redundant due to the use of electronic forms of payment.
The level of tracking from "I take out $400 in cash every payday from the ATM" vs. "I spend it in $10 increments on the following items" is wildy more invasive.
However since the transactions are cash, no identifying information will be shown, so it's anonymous.
As the buyer I have the CHOICE to declare it as a deduction or not. So it is also anonymous at my discretion.