Cars that have worn-out tires should replace them for better friction. You can insert a penny into a tire's groove with Honest Abe's head pointing in. If you can still see most of Lincoln's head from the side after inserting the coin all the way, you made need some new wheels, because 1/16 of an inch is the commonly minimum suggested tread depth.
If you have a bird bathtub or anything that you don't want algae growing in, place pre-1982 pennies into them, since their rich copper help retard algae growth.
You can exchange Canadian pennies for US currency at some banks or currency exchange locations. Alternatively, you can keep them as souvenirs or donate them to charity.
Old pennies
Five old pennies were commonly referred to as a "shilling." In British currency, a shilling was worth 12 pence, so five pennies would be part of that larger denomination. Additionally, in some contexts, five pennies could simply be called "five pence" or "five old pence" in reference to their value.
I believe the birch cent, the first pennies made in 1792
If the pennies were pre-1982 then 9 US pennies are very close to 1 ounce (9.145 pennies = 1 ounce). If the pennies are after 1982 then 11 US pennies are very close to one ounce (11.34 pennies = 1 ounce).
The US never made silver pennies. In 1943 the US made steel pennies. These are often mistaken for silver pennies.
The idea is to save copper pennies because their melt value is higher than face value. If the U.S. government eventually makes it legal to melt old pennies, then said hoarders can sell their pennies at a profit.
Two pennIes
Answer
US pennies minted in Philadelphia do not bear a mintmark, unlike those produced in Denver ("D") or San Francisco ("S").
The diameter of a US penny is 0.75inches. There are 256 pennies in a square foot
For US money-21500 pennies would equal $215. There are 100 pennies to a dollar.