Puppet generally produces metrics that only extend to 6 decimal places inside of a report. You can verify this by turning on stored reports, performing a few puppet runs, and examining the reports.
Note that all "metrics" extend to a precision of 6 decimal places.
However, occasionally, this is not the case. We've seen two cases where runs produce reports with data like the following.
Note that some of the metrics extend past 6 decimal places.
Normally, I can perform puppet runs all day and never see decimal places go beyond 6.