I was working on something as DO posted his solution...
.. a little longer but seems to work:
=10-MOD(SUM(IF((MID(A1,ROW($A$1:OFFSET($A$1,LEN(A1)-1,0)),1)+0)*(MOD(ROW($A$1:OFFSET($A$1,LEN(A1)-1,0))+1,2)+1)>9,(MID(A1,ROW($A$1:OFFSET($A$1,LEN(A1)-1,0)),1)+0)*(MOD(ROW($A$1:OFFSET($A$1,LEN(A1)-1,0))+1,2)+1)-9,(MID(A1,ROW($A$1:OFFSET($A$1,LEN(A1)-1,0)),1)+0)*(MOD(ROW($A$1:OFFSET($A$1,LEN(A1)-1,0))+1,2)+1))),10)
confirmed with CTRL+SHIFT+ENTER.
Note: I liked the 10-MOD() idea... so I borrowed that part from DO I was initially looking at using CEILING.. but that would require the whole formula doubled in length.
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