I always round like this: 
#round $num to 2 decimal places
$rounded = int(0.5+$num*100)/100;

[download]
That code doesn't seem to exhibit the strange behavior you see when sprintf for rounding.

In case you care about performance, the INT version I describe is more than 2.5 times as fast as the sprintf version: 

Benchmark: running RoundINT, RoundSPRINTF, each for at least 3 CPU seconds...
  RoundINT:  3 wallclock secs ( 3.15 usr +  0.00 sys =  3.15 CPU) @ 7753.02/s (n=24422)
RoundSPRINTF:  3 wallclock secs ( 3.21 usr +  0.00 sys =  3.21 CPU) @ 2906.85/s (n=9331)

In reply to Re: strange rounding behaviour by lhoward
in thread strange rounding behaviour by Anonymous Monk

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