He claims to have done that to avoid taxes, however that isn't why people do that. Anything deposited over $10K in cash requires a CTR - Currency Transaction Report. It's basically a report detailing where the money is coming from. Tellers also have the ability to fill out a SAR - Suspicious Activity Report. Any time a cash deposit of $3K or more is made and is deemed suspicious by the bank, they must fill out a report about the funds.