A different approach: instead of converting to unit prices and fiddling
with the display precision, just multiply the total prices by the same
multiplier (and keep them positive).
This seems a little more natural. I'm not sure if one of these will be
more robust than the other.
Transaction modifier multipliers have never multiplied total-priced amounts
correctly (and prior to hledger 1.10, this could generate unbalanced
transactions).
Now, the generated postings in this situation will have unit prices,
and an extra digit of display precision. This helps ensure that
the modified transaction will remain balanced. I'm not sure yet if
it's guaranteed.
