What you are probably referring to are partial fills. Say the ask is at .049 and you see a small fill of 1k on the ask. Don't assume that is a buy. It could be that someone has a sell order in at the ask and only 1k of that order filled.
Sometimes traders with large positions slap the ask with a small order just to raise the ticker price up a tick, especially in the final seconds of trading. That last trade makes the stock look better for the opening bell the following morning, and the ask may end up being one tick higher for the next opening bell. I see it all the time. Some brokers charge commissions based on the amount of shares bought, so people aren't necessarily paying $6.99 in commissions for a tiny trade like that
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