I'm not sure that it's a tradition now but when I was a bit younger, there was such a tradition: i remember that for sure it was at All-Russian Exhibition Center (ex-ВДНХ). Now as I know it is something like a tradition to throw pennies near Red Square at so called zero kilometer.

When I was skating recently at Poklonnaya Hill, Victory Park (Поклонная гора, М. Парк Победы) I saw hundreds of coins in the water (to the left off the hill)

I saw coins in the water at the pool though there are fountains too there. But I didn't look there.

I surely agree with mari an that the spread russian custom to throw petty money to fountains (rivers, grass, ravines, just on the street) means a wish to return there some day.