Why penny's should be banned?

Answer 1

The plural is PENNIES. Apostrophes are used for possessives, not plurals, as your English teacher should have told you.

Pennies should not be "banned" which means prohibited, or even abolished, so long as the U.S. has sales taxes that cause prices to be given in odd amounts. Other countries have successfully removed their pennies (or similar coins) from circulation because they have uniform taxes and laws that can enforce fair rounding practices, but the U.S. legal system isn't set up that way.

A number of analyses have shown that prices would all tend to round upwards, rather than going half up and half down, because stores would be afraid to lose money on single items.

Pennies are a problem because they are needed in enormous numbers due to odd-amount pricing and the lack of any denomination between a penny and a nickel - about half of the mint's production each year is pennies. The U.K. and E.U. solved the problem by making 2-cent pieces. That way you never need more than one penny to make change, and their mints only make about 1/3 as many pennies or 2-cent coins. However the U.S. has consistently rejected plans to make 2-cent coins, for no apparent reason other than tradition.