Lens box from another country - taxes and customs?

I bought my Canon EF 24-70 mm f2.8 a couple of years back from Singapore but when moving to the US, I left most of my stuff at my cousin's house. I've been thinking of selling my 24-70 since I want something even sharper . Used prices are higher in the US so I'd prefer to sell it here, but I don't have the lens box for it.

I'm going there for a vacation soon and I was wondering if I could put the lens box in my luggage when coming back to the US without incurring tax and stuff? I've heard advice for Brits going to NYC about bringing back electronics, so I'm wondering if the same applies everywhere. I'm not sure I'd like to pay taxes on a lens I've owned for 7 years!

I could try selling the lens over there, but the amount I'll get won't be as high and I'll be stuck without a lens. But if I were to buy a lens there (looking at either the 24-70 mk2 or 17-55), then the problem never ends if the time ever comes that I want to sell the lens when I'm in the states. Also, warranty worries, I'll prefer to buy the lens where I spend most of my time at.

Why not have your cousin fold the box flat and mail it here? That said, I doubt the box will make that much difference in your ability to sell the lens as long as you price it reasonably.