Generally small orders will not have any customs duty when shipped to USA. I have bought several items from Bike24 and other German sellers and never paid duty. One of those orders was my Rohloff, which I expected to have to pay duty on because it was close to a thousand USD, but I got lucky on that.

The only time I had to pay customs duty was on a bike frame that had a bunch of other bike parts in the box, the total value was over a thousand USD and was high enough that it tripped what ever threshold the customs people use.