In Canada, with sales taxes varing from 5% to 15% by province, we round to the nearest nickel on cash transactions. Non-cash transactions are rounded to the nearest penny as usual. Works fine IMO.
Note that the rounding is to the nearest nickel, neither up nor down. So it favours neither buyer nor seller; it all nets out about the same for all in the end.
We stopped minting pennies 10 years ago. They're still legal tender but rare to see since there's no need with 5-cent cash rounding conventions now. There were brief popular grumblings and misplaced arithmetic anxiety leading up to the death of the penny. I expect the same when we bury the nickel and I bet few will miss it either when its time comes. And then the dime.
Of course one can construct amusing temporary edge cases or arbitrage opportunities when buying specific quantities of specifically priced items in the presence of any new rounding rules. The market will respond.