I found this on a surname site (it lists Tasma as a surname)
TASMA 0 n/a 77307 - the first two numbers are meant to be frequency and rate and the last number is the rank (for the United States).
(also, in the BtN thread, a woman with Tasma as a surname says she is from the Netherlands so perhaps it is Dutch?)
Seeing as my last name is really rather rare in the states and it ranks just about 14,000... I'd say Tasma is a really super rare surname for the states but it is possible your Greant Aunt somehow heard it somewhere.
Plus, I found this really, really old BtN thread for the name Tasma (from 2001!) -