Quote SSRS calculations for new report style

I am creating a new report style that breaks out the total based on if a line entry is a certain part number. For example, if the part is “SS” then it is categorized as an optional service, otherwise it is equipment. So say there are two lines that are “SS”, each line being $133 for the total potential value, and two parts having a non “SS” line part at $2,117 for each line. The equipment breakout total would be $4,234 and the optional services would total at $266 with a grand total of $4,500 such as the below. The calculated fields are hidden per the generic ssrs report style, I need to know what the calculations are for the two totals and tax totals so I can re-create new calcs. Desired output below. Thank you for any assistance.

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I was thinking at first glance that I would try to have a piece of code or running total on each line that was accumulating the ‘SS’ extended price. Then I could alter the Equipment Subtotal to subtract out the accumulated value, and place the accumulated value into the Optional Services Subtotal.
Tax probably going to be a bit more tricky.