That's interesting. I also have a TDA account, which charges ~$0.65 per contract pretty uniformly. Are they paying the liquidity taking fees for me?
TDA is PFO on options big time and that's how it gets low fees. As far as I know, IB actually sends your option trades to exchanges unless disclosed otherwise. It used to own an option exchange Timber Hill before it closed it down citing conflict of interest (real reason I suspect is because it wasn't making money)