Flush timestamps are not aligned

When configuring statsite with a flush time of 10s I noticed that the flush timestamp it's not aligned.

I get these results (the result depends on the timestamp of statsite launch):

counts.test|4.000000|1468836448
counts.test|4.000000|1468836458
counts.test|4.000000|1468836468

And not

counts.test|4.000000|1468836440
counts.test|4.000000|1468836450
counts.test|4.000000|1468836460

Would be better the latter, wouldn't it?

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