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minimum bid is 5 cents
AFAIK a few rules has changed in the AdWords program. Have a look at their AdWord blog [adwords.blogspot.com], where it is written, they're
replacing the static USD $0.05 minimum bid for all keywords with a minimum bid that varies based on the quality of your keyword and ad text. High quality keywords (determined by the Quality Score) will have minimum bids as low as $0.01, while keywords with a lower Quality Score will be assigned higher minimum bids.
If I were you, I wouldn't be trying to figure out what's going on with individual clicks, I'd be working on keeping your average EPC stable or growing. I've noticed clicks on my site range enormously in value, but the average has stayed within a fairly narrow range for a year and a half. And that's fine with me. Predictability is a good thing.