$2.99 at 6.5% tax is $3.18 (after rounding). Buy two and your total cost is $3.37. The government don't not want to be cheated out of that penny. (it adds up over all the people buying stuff)
I genuinely can't tell if you are being serious. If you are being serious, then how do you account for the behaviour of the customer possibly changing based on how the price is displayed (i.e including or excluding taxes etc.)
Since in the US tax is traditionally never included in any state (exception: gasoline is always advertised with all tax), consumers are not changing behavior. I suspect there are a few who split purchases knowing the above, but for the most part few people do.
Also, you seem to be putting more thought into this than our government has.