COMPOSITION... Its not the first time I've seen coin shots, dpchallenge or otherwise, but I think this is one of the ones pulled off rather well. What makes this one work, in my opinion, are the way the colors complement each other and are pleasing to the eye. The central coin is distinguished against the rest by its difference in reflectivity and color. Lighting can be difficult with objects that are highly reflective but you really brought that property out on the main coin and the background coin in the lower left. Placing coin in the center? It was the best way you could compose this picture. Placing the main coin off center would probably the focus of the image - the coin could look like it was part of the background, weakening the composition by essentially killing off one of the image's focal points. All in all, very well pulled off and your score reflects that :).
TECHNICAL... My only concern here was that you went a bit too far with sharpening your photo, unless you didn't sharpen it at all and even then, I think the photo could have benefitted from a softer look. The camera is real good at picking up every tiny imperfection in the metal. How could you legally soften the image? Perhaps mostly by placing some fine gauze-like material over the lens before shooting - stocking? An old filter smeared with vaseline would do also...perhaps some diffused lighting might help as well, if you didn't try that... If you're interested in some non-legal dpc manipulations, I tried "ortonizing" the image above with very pleasing results (duplicate image layer, gaussian blur layer with ~ radius of 25, set new layer's mode to Overlay). It saturated the colors a little more and removed some of the imperfections... Even then I found that it still showed too much of the sharpening...I flattened the image, duplicated the layer, gaussian blurred that by a radius of ~ 10... then set the layer opacity to 66%...
Anyway, always good to experiment and try stuff out!
Good DOF. The center crop works for this pic. I like the way some of the pennies are tarnished a bit, some a lot, and some not at all. Gives this a little more realism. I would've gotten a brand new shiny quarter for the picture though. Great idea.