Some of them complicate things even further by charging you different commissions based on monthy volume (the more you trade, the less they charge per trade).
Anyway, nowadays most decent brokers, in one way or another, offer "fractional" lot sizes because they realize most retail traders can't properly manage an account with 100,000 lots because they are simply not as capitalized as a large institution and need the extra "resolution" or "granularity" that smaller lot sizes allow.
This can truly make or break you as a trader so your question is a very important one.