Okay, you keep saying that...how is it a search?
v. intr.
To conduct a thorough investigation; seek: were searching for clues.
n.
An act of searching.
Law. The exercise of right of search.
Idiom
How is it NOT a search? Are they not looking for something, in this case, evidence of a cash transaction in excess of $10K?
It's a search in the same way that it would be a search if the feds came personally into the place of business, searched through all the records, and wrote down everything they wanted to know. The only difference is, the feds are requiring the citizens to do the dirty work.
Suppose a law was passed requiring you to make videotapes of yourself at home--enough videos per week so that the feds could watch what you are doing 24 hours a day. Would you call that a search? Or is it only a search if they come and search in person?