Convert.ToDecimal(command.ExecuteScalar()) returns nothing

Here is my code again for the sp:

ALTER procedure [dbo].[presmetajSaldo]
(
@data DateTime,
@saldo decimal output
)
as

Declare @priem decimal

Declare @isplata decimal
 set @data='2012.07.12'

select @priem = sum(iznosden) from blag
where data=@data and vp>=0 and vp<=10

select @isplata = sum(iznosden)
from blag
where vp>10 and data=@data

update Kasovizvestaj

set

 saldo = isnull(@saldo,0.0) + (isnull(@priem,0.0)) - (isnull(@isplata,0.0))
where data=@data
select saldo from Kasovizvestaj
return

So the bolded line I suppose is the problem, which returns only the int part but not the decimal part (399.400). How to change it?