> pretty much any legislation on this planet would obliterate us if we'd tell them that the result of the computations of our systems may be some cents up or down from the real result

But you are not some cents up or down, even if you are calculating with billions, you still have 7 significant digits, that's a lot of head room for calculations.

Are there any financially sensible calculations where large numbers (order of magnitude billions) are multiplied with each other?