Quoting: Tlum
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".
or
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.