That's a precision of roughly 5 femtograms, or 510^-15 grams. This is about the mass of just the DNA in a single (diploid) human cell. Not the mass of the cell, not the mass of all DNA in the body, just the DNA in a single cell. A single human sperm cell weighs 2.210^-14 grams (22 femtograms). I'm not saying that maybe these scales aren't that accurate, but in a standard warehouse environment, there's no way that they need that level of precision, or, indeed, need that level of accuracy for this function.

I was originally thinking that it could be a final check to make sure the exactly correct item is going out with this order, but then I realized that the vast majority of manufacturers do not have this level of accuracy in their processes, also, a single dust mote would throw the scale off an appreciable amount at this precision.

Hold on though, I'm going to edit this if what I think is happening is happening.

Edit: Cool, here's a thing that might be happening: That mass is equivalent to 53.878 grams. This means that the scales are probably reading in metric to an accuracy of 1 milligram. This is plausable for a small item scale. In fact, here's a pocket scale that could do just that for a little over $20 on Amazon. The scales at Amazon are more than likely automated, too. This was most likely converted to pounds for shipping in the United States.