I work in the financial sector. In the summer months especially, it is common to see women dressed in sleeveless tops. I would argue that sexualizing one's peers is much more unprofessional than dressing for comfort.

Tank tops seem to be pretty normal in jobs where a lot of young women work (except in positions that deals directly with customers). Judging by what I have seen women wear last year.

If it seems too revealing to someone, that someone is probably spending all time with males or old women only.