Yes, it can be but sales tax is confusing in the US due to city tax, local tax (MTA in NYC, for example), county tax, state tax, etc. They are always changing too, amounts and types of items taxed. Your Big Mac costs 100s of different prices across the country. So its often easier and cheaper to just advertise the pre-tax amount (especially in national ads) and program the register to handle tax.

But you are right, it is also preferred to hide some of the costs. But, sometimes you get a place that includes taxes on the price. Very refreshing.