$10k is the number that banks have to report.
So I have heard...along with much lower numbers. The funny part is that the transactions most likely to trip flags for me are transfers to ....write out checks for quarterly taxes.
$10K is the number banks HAVE TO report. They CAN and are ENCOURAGED to report ANY cash transactions of lesser amount, if that transaction seems out of the ordinary for the customer, or there has been a set of cash transactions in the near past.