Unfortunately I think this is much easier said than done. No single store is going to want to make this change, because it'll make their prices look higher than the competitors'. It'd require legislation, (and even that'd likely be state-by-state legislation).
It also means a company wouldn't be able to advertise a single price for a product nationwide, since sales tax rates vary by state (and many times even within a state).
Also worth noting that Canada also doesn't include sales taxes.
It gets tricky because sales tax is added on top of the sticker price.
Then include the sales tax in the sticker price, like every other country does.
Unfortunately I think this is much easier said than done. No single store is going to want to make this change, because it'll make their prices look higher than the competitors'. It'd require legislation, (and even that'd likely be state-by-state legislation).
It also means a company wouldn't be able to advertise a single price for a product nationwide, since sales tax rates vary by state (and many times even within a state).
Also worth noting that Canada also doesn't include sales taxes.
The statistics on consumers evaluating the purchase of something that is $9.99 vs $10 is well proven.
Switching to round number prices would cost retailers a whole lot more.
https://www.sciencedirect.com/science/article/pii/S002243599...
https://www.researchgate.net/publication/23547242_Penny_Wise...
https://www.sciencedirect.com/science/article/pii/S002243590...
The rounding is applied to an entire-after tax bill, not to shelf prices.
Again: Canada actually did this many years ago. The effect you predict did not appear.