I would expect that, like most other things, competition on price
alone would be ineffective.
If they are in the same consignment shop, B might have the edge.
If A is next door and B is across town, B's price is never seen.

So?

Rounding UP makes the calculations easier for everyone. At worse, it will
cost comsumers $.04 per item.

Add it up if you will. The most lazy and stupid consumer might pay an
extra $50 the first year. After a year things will sort out.