Cannot perform summation if grouped results in Report Definition

We need to perform summation of a column in report definition (displayed in report browser) with group by on few columns. As soon as we are putting SUM option for the column, we are the losing the group by option in the Report Viewer and the look and feel gets lost.

How to sum grouped records or total summation of all records in a column without losing the look and feel.

Attaching: Expected -Business requirement to group on few columns and sum the cost

Actual_1: In case of putting sum, the group by is getting lost.

Actual_2: Without putting Sum and using group by in Report Viewer Tab ( summation of cost option not happening)

***Edited by Moderator Marissa to update platform capability tags****