Here's how to tell the difference between the Plain 5 and Fancy 5 1865 Two Cent pieces:
Plain 5: the top edge of the 5 appears flat or slightly curved
Fancy 5: the right half of the top edge of the 5 dips dramatically, creating a distinctive "flip" to the point of the 5.
Sources and/or recommended reading:
"Getting Your Two Cents Worth" by Kevin Flynn
"Two Cent Piece - An 1864 Attribution Guide" by Frank Leone
"Cherrypickers' Guide, Fifth Edition, Volume I" by Bill Fivaz and J.T. Stanton