Nope, one dime. Because think about it, the wheels don't deform THAT much when they contact the rail, which means that, essentially, the wheels are touching the rail at a single point.
In order for each wheel to have a dime sized contact point, they'd have to flatten out quite a bit.
I've heard its a dime per wheel. But anyways, here's the formula to figure it out...

Or you could just wake up and realize that the static frictional force does not depend upon surface area...
Now, why, would I want to do that?