A wild guess just for fun! Cue all smarter folks to line up and show how inefficient this query is!

SELECT TAB1.SalesOrderId AS ID1,

TAB1.TotalDue AS DUE1,

TAB2.SalesOrderId AS ID2,

TAB2.TotalDue AS DUE2

FROM SALESTABLE TAB1

CROSS JOIN

SALESTABLE TAB2

WHERE TAB1.SalesOrderID <> TAB2.SalesOrderID AND

TAB1.TotalDue + TAB2.Totaldue = @SPECIFIED_DIFFERENCE