Use Aliases In Calculations
Another approach is you can layer your queries as sub-queries, which allow you to capture all results, like so.  Also you most likely wanted to use "sum" instead of "count".

select Rpt1, Rpt2, Balance = @totalsales-Rpt1-Rpt2
FROM   (Select Rpt1 = sum(case when empID = '1931' Then 1 else 0 end)
        ,      Rpt2 = sum(case when empID = '1831' Then 1 else 0 end)
        From totalsaleinfo
        Where saleid = @saleid) AS sums