

Danny!
Finding full steps on 90s nickels is pretty common, so when I'm culling them out for saving, I also require few scratches, digs or dings. I'll sort them, save them, then go through the pile to keep the very best and put the rest into circulation again. The 1975 w/o a MM is a Philadelphia minted coin. About twice as many nickels were minted in Denver (noted by the D), but still a pretty common nickel to find in circulation. A nickel from this period has to be showing 3-4 steps with few digs or scratches to get my consideration. As for the nickels reverse designs, these change/changed periodically, sometimes subtly and other times profoundly (like the 2004s) so learning how the designs differ will take some time and researching. The same is true on many coins; obverses and reverses. The 1968D could have a double die obverse, so you'll need to give that a closer look.
So enjoy the hobby; read posts (use the Search tool and insert key words/terms) and ask questions especially here at CCF!