Sharon's Tatted Lace

It's a mystery. This afternoon I was intrigued by several shiny discs glinting on the back patio stones. They appeared to be about the same size as the plugs we removed from the junction box when we wired in the downstairs lights. There was no way the plugs could have gone from the garbage pail in the garage to the backyard, so I sent Rob out to investigate. He came back in with 3 shiny quarters. How do quarters get dropped onto the fenced in patio when no one has been in the backyard?
Three was an odd number so I sent him out to look again for the fourth quarter. He came back with 2 dimes and a nickel. Curiosity fully aroused, I went out to see this phenomenon myself. Scattered over our yard, on the lawn,in the flowerbeds and around the outside of the fence $3.70 in nickels, dimes and quarters but no pennies.
Our first thought was that the grass cutter had lost it out of his pocket, but why no pennies and why were they in the flowerbed. Even if you back up to get the lawnmower into position you don't stand in the flowerbed to do it. That explains why there would be coins on the patio, but not the flowerbeds.
Did the tooth fairy lose the coins during the night. Did someone in a fit of exuberance throw a handful of coins in the air to land where they may and if so, why only in and around our yard not in the back greensward or the neighbouring yards?
I expect we'll never know, but it would make an interesting plot for a story.