Two options:

1) Use a scrolling region. This allows your table of items to scroll without the total (which is outside the scrolling region) moving.

2) Place the total in a location that won't scroll--such as above the table. I know that's not very traditional, but it would not move.

I need to lock a "totals" section from moving down the page if I choose to
use an optional section for notes in the body of a Purchase order form, or if
I have more than one line item.  I am new to InfoPath and could not find it
in the help.