Maybe you can try to save GNUCash ledger onto MySQL database instead of text file and see if precision improves. It can happen that the devs stored numeric as string to simplify adaptation (toSQL), in which case there be no improvement on precision.

ledger-cli makes it difficult to assign the task to an accountant. all successful investors ends up hiring an accountant - since you invest in Bitcoin, chances are you will be successful and will hire an accoutant, and end up either switching away from ledger-cli or so rich that you hire an accountant who were trained in Unix too:)