Table tool in BIDS/SSDT is used to show the detailed data. It is not used to show the summary data. This is shown in the image below.
In the image above countries names are repeating many times for each sale.
But you can convert the detailed report into summary report as shown below where country names are not repeated and we are getting total sales.
I am writing the steps to convert detailed SSRS report into summary report.
In the figure below three lines which I have encircled represents the detailed section of the report. It means it will just display the records as it is present in the source table. Now right click on the Details under Row Groups and click Group Properties as shown below.
Under Group Properties click on Add and then in Group On dropdownlist choose SalesTerritoryCountry as shown below.
In the figure below you can notice that detailed section (three lines) has been converted into group (single line). Now I need to display sum of Sales Amount for each country. For that right click on the cell of SalesAmount and go to Expression as shown below .
In the Expression window write =sum(Fields!SalesAmount.Value) to display sum of Sales Amount for each country as shown below.
Now go to preview and check the result. This is like converting tablix report into matrix report in ssrs