Report Builder supports Running Total Field Calculations. You will find this feature helpful in reports that involve tallying totals within or across specific groupings.
To explain further, let's take a look at our example report.
If you right-click on the field, you will see you have the option to set as a running total field. This will give you the option to calculate the data in the selected field:

In our example, we chose to take the sum of the running total field. This is how it will show when you preview the report:
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