When we selected any month in parameter then running sum will show correct sum in row.

Step:1

Create parameter with month like integer 1,2,3,etc

Step:2

Create calculation [Running sum of month total]

if [Month]=12 then (if last()=0  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=11 then (if last()=1  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=10 then (if last()=2  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=9 then (if last()=3  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=8 then (if last()=4  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=7 then (if last()=5  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=6 then (if last()=6  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=5 then (if last()=7  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=4 then (if last()=8  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=3 then (if last()=9  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=2 then (if last()=10  then (RUNNING_SUM(SUM([Sales])))end )

elseif [Month]=1 then (if last()=11  then (RUNNING_SUM(SUM([Sales])))end )

End

Step:3

Drag the month in to row.

Drag this [Running sum of month total] calculation into row

Step:4

Drag this [Running sum of month total] into filter and apply non-null values.

Step:5

Show parameter control and select months.