Report it in barrels to two decimal places. Basically come up with some number "as close as reasonable" that you can replicate and justify in an audit. And keep a copy of your calcs to have as proof of how you came about these numbers. Creativity may be required.
If you don't feel comfortable that your methods or documentation can withstand scrutiny,(or don't know what it is), just leave the box as zero and pay the tax...it may not be that much.
The totals, both horizontal and vertical, are just that-totals from above or from the left, as added. Yes, the form is somewhat redundant.