American Indians and payback?

So I have a meeting with a client at the Mohegan Sun Casino this morning and as I am leaving, I realize I have no gas. I pull into the station, still on the reservation, slide my credit card and it is as that point that I realize the price per gallon.

After I put just enough gas in to get me home, I started to wonder how they could justify this price given the avg ppg is right around $3.75 - the sign also struck me as odd in that is claims that all taxes are included. Why are they collecting taxes...it's a reservation??? Is this our payback for plundering the Indians?