Nope. It's for customs, not immigration. You're already in the country, they just need to figure out whether they need to search your bags for contraband.
That's the point. If you refuse then they do a thorough search.
If you answer suspiciously, or refuse to answer, then you get the full search.
This is similar to how you can refuse body scans at the airport, but if you do then you get the full pat down search.