I think it's short for "está". When I first heard my wife speaking portuguese on the phone she kept saying what sounded like "ta-bye, ta-bye" so I asked her what it meant and she said it was basically "yeah, OK" - and it's just "está bem" said in a Madeira accent. I've come across it in comics too. A character with an accent will often use it.
Obvs I'm not a native speaker so apply liberal salt-pinches, but that's what I've gleaned!