Yeah, tangs get way too big for a ten gallon and like chris02 stated, I wouldn't try anything less than a 29 gallon.* Get the biggest you can afford and accomodate.* All fish need stable water parameters, but Saltwater fish even more so and having a smaller tank results in more fluctuation with those water parameters.*
I'm not saying you couldn't keep a 10 gallon saltwater tank, just that it will be more difficult on you as far as maintenance and testing goes and you really limit yourself with fish selection.
http://www.fishlore.com/Profiles-YellowTang.htm