There have been some cultural rituals or customs with money or other symbols of wealth over the last billion years and I guess everyone has their own even today. We leave flowers at graves, I'd think coins are pretty much for the same reason. Just an individual or regional thing. I think my friend was asking about pennies because these were graves of Confederate soldiers and she (being a true Southern girl) thought Lincoln's face shouldn't be there. Like salt in the wound. Of course, nowdays a quarter could be left because it's about the same real value as the penny. Maybe the penny has more. Copper is up. ??? Hubby's always told me to put a penny in his pocket (so he wouldn't be broke) and his que stick in his hand. My family knows I better have a Battle Flag on my person or I'll be a comin back to haunt em. Just sayin--- :)
My Grandmother once told me that her Mother (the mortician) said coins were used to keep the eyelids closed.