We already pay for things rounded to the nearest cent.
For example, gasoline is priced to the mill (that’s the extra “9”), but you pay in full cents. Likewise, any percentage, as for taxes or commissions, can easily produce fractions smaller than one cent, but these are rounded with no objection.
So nickel rounding would be the same. All products will be priced to some multiple of five cents. When taxes or other calculations are applied that produce any other result, it’s rounded up in favor of the seller (this is the way gasoline works now; $18.753 rounds to $18.76).
There’s no reason for electronic transactions to be any different than cash transactions.
Actually, what would make the most sense from the internal logic of American currency, would be to drop the cent and five-cent coins, and make the dime the smallest unit (like it says, “ONE DIME”).