You have to admit, you don't usually anticipate having fun with a progress bar. Thankfully, Nintendo does.
There are a few variations where Mario makes his way across the screen, collecting coins and bumping blocks. It's light, it's fun and in one case, you can even shoot fireballs yourself while he runs. Suddenly an uninteresting part of the shopping process is fun and engaging to the user.
It's another example of Nintendo's whimsical attitude towards its product and its customers, and only reinforces the family friendly brand voice of the company.