The only charms I've washed have been batiks and they didn't need it. I am washing fabrics less now if I am confident of the quality. I do wash WalMart fabric and JoAnn's solid quilting cotton - they just haven't got that one right and it's the same price as Moda at the LQS. I had to buy a piece recently to get the color I wanted. I lost 2" in width. 5% is too much shrinkage. Now I'm going to wash a quilt store one for comparison.
I've always been a fabric washer, so my first pack of charms was an experience. I did soak one in hot water and put in the dryer. It was still 5".