There's an entire thread for this discussion already, please use the search function before posting duplicates: http://forum.square-enix.com/ffxiv/t...n-of-Etiquette.

On topic: If you are the tank, you're prefectly entitled to roll Need on tank gear, even if you end up not using it. You brought the class into the run, so the loot is your if you want it, thats how the system works in this game. There's of course some player made etiquette, but if you read through the thread I linked, everyone seems to have a slightly different take on that.