I personally think terms such as "penny", "nickel", "dime" and "quarter" are all slang terms for our coins valued at 1¢, 5¢, 10¢ and 25¢ respectively. I know the term "nickel" was due to being originally made up of nickel (and may no longer be the case today), and the term "quarter" was due to being a quarter of a dollar. I am, however, interested in finding out where the slang terms "penny" and "dime" originated.
The slang term "loonie" is due to the presence of a loon (a bird) on one side of the coin, and the "toonie" is more a replacing of the L with a T, plus it corresponds with the $2 value.
Amazingly, even credible news sources, such as CBC, use such slang terms when doing reports about coins.