Box plot, also called box-and-whisker plots, is used to show distribution along axis. It usually has one Dimensions and one Measures on Columns and Rows respectively. Although the "Show me" feature in Tableau can create a box plot only with a click, I will demonstrate how to manually make on in this blog post.
Move Category to Columns and Sales to Rows
Change Marks card to Circle
Drag Region to Details
Click on Analytics tab. The Box Plot option should now be available. Click and drag it to the canvas, drop it on Cell
The Box Plot window will pop up likes this:
Format border, whisker, and color as preferred. I also decrease Opacity of circles to see the box plot more clearly.
You should now have a box plot that looks like this: