This is not a question, just an attempt to try & prevent other users falling into the same trap that I did!

When entering my first batch of journal entries I found that a lot of supplier invoices had (slightly) incorrectly calculated the VAT.

Odoo does not offer any way to deal with this that I could find but I did find that altering the decimal precision to three places helped.

End result; nearly half of my entries were unbalanced.  Fortunately, a retrospective edit of Decimal precision back to two places sorted the problem.

Although after the edit, the affected entries (which were now balanced) were still being reported as unbalanced the post worked ok.