Unless you're reporting the values in bytes, there's going to be rounding or truncation done at some point. When it happens is down to your needs/preferences. It's hard enough to get people to agree on whether they're calculating based on powers of 10 (marketing) or powers of 2 (nerds
), never mind the significance of the decimals after you convert the bytes to gigs. (Personally, I've largely given up on that fight. Decades of one voice trying to out-shout an avalanche has proven fruitless. Marketing has won.)
Generally speaking, for my needs, at least, when I'm reporting disk capacities in gigabytes, rounding to the gigabyte is accurate enough. If I need more accuracy, I'd either drop the rounding, as you suggest, or more likely report in megabytes (or kilobytes, or bytes, as appropriate to reflect the level of accuracy needed).
As for the labels on your adjusted output, if you want to be accurate they should read "MiB", not "GB". If you want the results in GiB, you'd need to use Power(2, 30) or Power(1024, 3).