I would dispute this one for sure. The hotel is circumventing the way many booking engines would show it by hiding it under taxes.

I assume this is not illegal, because hotels can get away with all sorts of deceitful practices and nobody seems to care. However, I'd still dispute the hell out of it.

And since Hilton's own website classifies it as a tax, I'd probably also send a note to the local tax authorities. (Not that I really expect anything to come of that...again, local governments in general seem okay with hotels basically doing whatever they want on a wide variety of issues.)