How do I rond three decimal places?
Look in the 4th decimal place. If it's less than 5, just truncate the number to 3 decimal places. Otherwise, add 1 to the 3rd decimal place and then truncate.
5.3063192 -> 5.306
12.909762 -> 12.910
5.3063192 -> 5.306
12.909762 -> 12.910