They are also called on occasion "Lollipop Tangs"
I use to have one. Very cool fish.
Yours can be of several Acanthurus species. I have not seen one with the blue strip across the top yet and might be just a marking from it's juvenile stage.
My first guess would be the common Powder Brown 'Acanthurus japonicus'
The white tail also resembles the Goldrim Tang 'Acanthurus nigricans'
Either way, it is a nice fish. I would not worry to much about the tail yet. Eventually it will take over the tank as the new terrorist