"Ironically, we did penny tile in both of our bathrooms. As to the “how” of this project, you can get mesh backing that’s adhesive on one side. Stick all the pennies to that, in 8” or 12” squares, then lay it down in grids like any other tile that’s similar. Grout it & voila! Pretty cool effect, but the anal retentive in me badly wants of them heads-up & facing the same direction!"