Follow these steps to create groups:
1. Right click on the field that you want to make groups.
2. Select create New Group.
3. Select bins/ list.
4. You can select the number of bins or size of bins to create bins.
4. Enter size / number of bins and press ok.
5. Now you can put the bins in filter to see respective bins (groups).
As per your problem, you can make 3 bins on sales so that you can see below 33.33% and above 66.66%.
Now apply the group in filter and select the bins 1 and 2.To show the bin details, drag the bin to values to see the bin it belong to.
Hope this helps you.