Yes banks do report all cash deposits and the amount of money that you have or have had in your bank account for the year.
At the end of the year all banks are required by law to report your bank account amount or any cash or check deposits as well as direct deposits to the IRS.
So just depositing cash won't get you off from the IRS as they will be notified by the bank on the amount of cash you deposited no matter how small the amount of the cash was.
If you deposit $10,000.00 or more in cash at once then that amount gets reported to the IRS immediately.
If you deposit $10,000.00 or more daily or weekly and haven't before then the IRS will likely audit you and the bank may investigate just to be sure there's no bad activity going on.