1024000000 = 976.5625 MiB, why use 976 not 977

I would like to give some feedback about ... 1024000000 = 976.5625 MiB, It should approximate to 977 MiB, not 976 MiB. But the test use 976 MiB as correct result, what's the reason? From: https://py.checkio.org/mission/friendly-number/solve/

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