Your bank will report interest via the 1099-INT, and they will do this if you make more than $10 per year. You will also get a form if you redeemed any government bonds. I'm not deeply familiar with AML/KYC, but transactions over $10,000 are reported to the government, but not necessarily to the IRS and definitely not as a taxable event.

Let's say you sold your car and deposited the money in your account. The IRS won't have details about the sale and neither will your bank. They will know the amount, but it is incumbent on you to report information if this sale represented a capital gain. In all likelihood it wasn't, but the government doesn't have a way of knowing this. If you get audited, someone will probably ask where the money came from and it would be up to you to furnish receipts in order to prove it.