The government does not have to right to tell a seller how much to charge, or how much profit to make.
I have also seen signs at convenience stores here in PA saying lowest cigarette prices allowed by law.
I also have to wonder if it also has to do with the state and or local governments feeling they are being cheated out of sales tax revenue.
The Idaho (ID) state sales tax rate is currently 6%. Depending on local municipalities, the total tax rate can be as high as 9%. Local level, non-property taxes are allowed within resort cities if approved by 60% majority vote. This includes hotel, liquor and sales taxes.