Mercury Dimes and Buff. Nickels are notoriously famous for showing mechanical/ejection doubling. Not a doubled die, and there is no numismatic premium for them. They are very very easily found in pocket change, or any group of older coins too.
First, welcome to the neighborhood @ahousefavor ! As a rule, when the suspected doubling appears to be "flat and shelf-like" you can pretty much bet your sweet bippy that it is machine doubling (aka mechanical doubling, strike doubling or ejection doubling). Chris
