Usually, in German we use "egal" for "I don't mind either way", "I don't give a f***" or "Whatevs"
e.g. "Möchtest Du lieber Obstkuchen oder lieber Käsekuchen?" - "Mir egal"
It would sound rather weird if you said "Wie auch immer" in this context - at least to me, but then I'm probably your granny's age.
"Wie auch immer" is ONE possibility of saying "Whatever (you do)" - Note: if you want to use it with "tun", it's "Was immer Du tust"!
Usually, "wie auch immer" is followed by a sentence in German, or at least by some sort of conclusion:
"Wie auch immer (Du Dich entscheidest), einer wird Dir böse sein" =
"Egal wie/für wen/wofür Du Dich entscheidest, einer wird Dir böse sein"
Regards,
Susanne