It's interesting from a purely computational perspective, but I'm pretty sure most people would have some difficulty counting out in denominations that aren't mod 5.

Noting that this is from 2003, before many stores introduced the automatic changer, I'm not sure if the 17% increase in efficiency would make a huge difference.

Humans themselves aren't efficient, and many registers across America aren't designed to be an assembly line with no niceties.

One would think the 50c coin would be in wider circulation than it is, so I'm assuming the authors are correct that the odd denomination wouldn't see large acceptance.