Complex sentence: The "small blind" is normally half the big blind, in cases where posting exactly half the big blind is impractical due to the big blind being some odd-valued denomination it is rounded down to the nearest practical value.
Split into simpler sentences: The "small blind" is normally half the big blind. In cases where posting exactly half the big blind is impractical due to the big blind being some odd-valued denomination, the small blind is rounded down to the nearest practical value.