I'd say "niewazne" or "cokolwiek"
It's good translation for 'whatever' word but it isn't used in similar context. Ekhm, it's hard to explain.. when you say in English for example:
Whatever happen i will be with you.... then Polish translation will be 'Cokolwiek sie stanie bede z toba', but 'cokolwiek/niewazne' isn't rather used as single word sentence.
Sample sentences with whatever from wikipedia en.wikipedia.org/wiki/Whatever_(slang):
Mother: "You must clean your room before you go out?"
Son: "Yeah, whatever".
Friend 1: "So we can meet at the bar before we go to the party?"
Friend 2: "Sure, whatever".
'Niewazne/cokolwiek' wouldn't be used as a respond in this cases.