In basketball a dime is an assist as in “Russell Westbrook drops dimes all day.” That was bad. I’m sorry. Anyway, if you’re like me, you’re still confused at how the jump was made from assist to dime. I’m going to tell you where it originated, but I’m going to preface it by letting you know this explanation is a STRETCH.
It *supposedly* refers to a person dropping a dime in a payphone to tell the police about a crime. As in, by dropping said dime, the person has now assisted the police. Just let that sink in for a while.