You need to use sprintf or printf. 
  $unrounded=0.66666;
  $rounded=sprintf("%.2f",$a) #$rounded is rounded to 2 decimal places
+ and is equal to 0.67
  printf("$unrounded rounded to 3 decimal places is %.3f\n",$unrounded
+);

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You might also want to take a look at floor and ceil

In reply to How do I round a floating point number? by vroom

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