SSRS totals by runningtotal

I am displaying the follwing,
Store Group <Group>
Store<Group>
Category Sales
Chair     $10.00
Table     $20.00
Store Total $30.00

Store<Group>
Category Sales
Chair     $8.00
Table     $16.00
Store Total $24.00

Store Group total $54.00

I want to show the category total for each category as the folllowing,

Store Group <Group>
Store<Group>
Category Sales
Chair     $10.00
Table     $20.00
Store Total $30.00

Store<Group>
Category Sales
Chair     $8.00
Table     $16.00
Store Total $24.00
Store group totals by category
Chair $18.00
Table $36.00
Store Group total $54.00
Can you please let me know, How to do it?

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K.Athma