Welcome to CT! That little letter is a mint mark. D=Denver, S=San Francisco and P= Philadelphia. I don't know when Philly started putting their MM on coins, but they didn't put it on in 1970. You have a common 1970 P dime. BTW, one post is enough. More than one is frowned upon here.
You have a normal Philadelphia minted coin. Worth face value. The coin you are inquiring about is a proof only issue that was minted at the San Francisco mint but lacks the S mintmark
FYI - There are several Proof Sets that have a coin missing the San Francisco (S) mintmark. They are: 1968-S "No S" dime 1970-S "No S" dime 1971-S "No S" nickel 1975-S "No S" dime 1983-S "No S" dime 1990-S "No S" cent