When I came back from overseas, and you return back to the US, the customs agent will ask you if you have anything to declare. If you did a bunch of shopping, it's best to say you have items to declare. God forbid they ask you to open up your bags for inspection, and see the purchased goods, you may get the goods confiscated and/or be hit with a penalty fee. You're usually allowed $800 worth of merchandise without having to pay duty. Anything over that, you'll need to pay taxes on.
