In the US banking system, that's called structuring. Which means that transactions of $10,000 or more are legally suspicious, and transactions under $10,000 are legally suspicious.
Logicians, please simplify the previous statement.
You are incorrect: "Transactions under $10k" are not legally suspicious, but rather, multiple transactions that are very large but under $10k but when added together are more than $10k. It's not that easy to end up under scrutiny for structuring unless you're running a cash heavy business without declaring it. Moreover, 99% of the time, the "scrutiny" is "fill out this paperwork"
I stand by my statement. Are banks required to scrutinize $10K+ transactions? Yes. Are banks required to scrutinize <$10K transactions to determine whether they're really $10K+ transactions? Yes.
Compare: in the US, you can be detained for driving over the speed limit. You can also be detained for driving under the speed limit, if police believe either that your slow speed is dangerous, or that you are driving slowly to avoid being detained. In all but the most egregious cases of abuse, a driver will have little reason to complain that they shouldn't have been pulled over.
https://en.wikipedia.org/wiki/Structuring