Many people do not realize there is a miniature Lincoln inside the memorial building on the back of the penny coin. Examined many pennys with 15x magnifier to find one with minimal dirt and scratches, cleaned best one, tacked it with glue stick to paper to keep it from rolling. Used 105mm lens + 3 ext. tubes, endless fiddling to get penny exactly square to the lens, focusing rail, exposure delay to minimize vibration. Getting detail to show took a lot of experimenting with light, finally settling on flash diffused about 45 degrees camera right, constant light diffused overhead, LED light slightly camera left, white paper to far left and below coin. Three lights, 2 difusers, 2 reflectors for what I thought would be a "simple" image.
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This is a tough shot, but it doesn't look like your lens was parallel to the coin, producing uneven sharpness. A higher f number might have helped. Excellent lighting.