round up conditional formatting bottom 10%

When you choose the bottom 10%, that is the bottom 10% of the values and the number of values formatted will change with the number of values present.

Instead of using Bottom 10% try using Bottom 10 items. You can change the number in the dialogue to what you want when .

If you are actually wanting the bottom 13%, you can change that in the dialogue box after clicking on the bottom 10%.