Try to purchase anything using over $10k in cash and see what happens. Multiple payments of $9990 in cash will get you busted for money laundering too unless there’s a judge in the family. Ask Beto,he knows.
Amounts much less than that trigger "structuring" meaning that trying to adhere to the law of not carrying more than $10,000 shows you're trying to skirt the law by not trying to break the law. Crazy! People have lost their money to seizing for carrying thousands less than the $10,000 trigger. Because government says you meant to break the law, even if you didn't.