What is the reason for finding dimes?

Not all things can or should be interpreted as omens.

At one time, money was worth a lot more (people worked for much less) so they would take the time to pick up loose change when they dropped it, or saw it on the ground. These days a dime doesn't buy much and people don't tend to care much if they drop one or two. If you check, you may find the dimes are found in and around places where people are looking in their pockets for change, or putting change away. This is most likely your explanation .