The Rice University Neologisms Database

a perfect girl or woman. May also refer to an excellent object. A dime, being worth 10 cents has come to represent the number 10 in this case it refers to the highest level on the oft-referenced ‘female rating scale’ from 1-10. It has undergone an odd derivation, essentially coming from using the usage of the word ten as in, “that girl’s a perfect ten” and then applying the drug-user slang for 10 ‘dime’ to that context. It has thus undergone metonymic shift. In even more recent times, it has undergone widening to refer to anything that is seen as perfect, or nearly so enough to be classified as a ten out of ten.