Every ATM knows which bill has been distributed to which card holder. Said number is recorded again once it's brought back to a bank - plus the account it's deposited to.
Sure, you can't trace each bill immediately, but as one doesn't deposit or withdraw a single bill at a time, a large pile of data is created. And, with said pile: Patterns and connections. The rest is just Business Intelligence and Big Data Analysis. But, in the end and with sufficient data, one can determine each and every probable connection you might have had and each place you contacted for a transaction. Even those that do their very best to stay offline - everything hidden in the big data spiderweb data fields.
Anonymity is an illusion. It's just a matter of time, effort and reason to look into one's details. Don't give them reason to suspect anything and they won't use these tools....yet