Just print each piece once and you'll have a traditional 28 set of Dominoes

I just added a domino holder to view your tiles while playing. It's a little oversized on the X-axis, so I recommend scaling down to 90% and keeping Y&Z at a 100% to get the dimensions as pictured above. Note that it can hold a total of 8 dominoes sideways. However, you can fit 8 across the top row alone, and 4 along the bottom and still see everything. If you print 2 of them, they stack together to form a cube shape for storage.