That my friends is the key. The lowest valued coin available sets the rounding point. When we had 1/2¢ coins, we could round to 5 mils. Now we round to 10 mils, and if we eliminate the cent we would round to 50 mills, etc. You can make every combination from 1-99¢ with only the cent, or the cent and the nickle, or the cent, nickle and dime, or the cent, nickle, dime and quarter, or the cent, nickle, dime, quarter and half. Stopping at the quarter is the most efficient combination, balancing bulk, weight, and convenience of counting. If it wasn't the cause, at least the bulk and weight of the half enabled the group decision to abandon it on the rubbish heap of history.
It appears that financially, all of the denominations have a use, and thus exists an argument that the cent and nickle should remain. It would seem then that a change in composition would be the way out of the problem. As was said in "The Graduate"~Plastics. Sure, a metal coin could last as much as 25 years in circulation, but more and more stores have a cup of free cents to make up a difference between 1-5 cents on a purchase, and more people are leaving the extra cents instead of pocketing them with the extra change, so why not make the cents in plastic, different colors, special combos of colors. People would collect them out of circulation before they wear out. Maybe 50 diffferent colors per year. TPG could label them MS70 First Molding, Errors would be colors swirled rather than just one, the numismatic industry would soar, new books, new folders, new hype, and the old cents would disppear and I would have to buy real washers from Home depot(tm). AIMHO.
Isn't it true that in some countries, the various taxes are built into the price? That is, the price on the item already includes the tax. So it's not, say 2 dollars plus tax, it's 2 dollars including the tax. I thought Australia was one of these countries, and they eliminated their penny/cent many years ago.