The pentagon.
A confederation
There are no square nickels. All US nickels are round, and Canadian nickels are either round or dodecagonal (12-sided). Please check your coin again and post a new, separate question with its date and country of origin.
A US "penny" is actually a 1 cent coin, worth 1/100 of a dollar. A British penny (the coin's official name) is worth 1/100 of a pound sterling.
The US 10 cent coin has president Roosevelt.
No circulating US coin has 11 sides.Early designs for the Susan B. Anthony dollar (1979-81 and 1999) had 11 sides. However the final design had a standard round edge with an 11-sided interior border. The US Mint felt it was impractical to strike a multisided coin despite the fact that other countries had been doing so for many years.
Nonagon is the name of a 9 sided shape. The US Steel Tower in Pittsburgh, Pennsylvania is a nonagon.
...Of what US coin? There have been several US coins intended for circulation ranging from half a cent to $20.
A quarter
dime
the nickel.
The nickel.
the biggest is the dollar coin and like its name it's worth a dollar
The pentagon.
the first us coin was the pine tree shilling
eagle
Franklin D Roosevelt