SSAS / MDX Query - Need row total
Try adding the All member into the set on rows:

SELECT 
  NON EMPTY 
    {[Measures].[Order Count]} ON 0
 ,NON EMPTY 
    {
        [Date].[Year].[Year].ALLMEMBERS*
        [Date].[Quarter].[Quarter].ALLMEMBERS*
        {
          [Order].[Customer].[Customer].ALLMEMBERS
         ,[Order].[Customer].[All]
        }
    }
  DIMENSION PROPERTIES 
    MEMBER_CAPTION
   ,MEMBER_UNIQUE_NAME
   ON 1
FROM [Order]
CELL PROPERTIES VALUE