Today I was presented with an interesting issue. A clients database where they kept sales records and VAT information had a small rounding issue. Things were not being rounded up or down to their liking. With a VAT rate of 17.5% a lot of values were ending up with a figure that was accurate to 3 decimal places with the third decimal place always being a 5 for example 125.255.
When displayed with a currency field that is set to only display 2 decimal places it will get rounded up to 125.26. but if it was a value of 125.225 it would get rounded down to 125.22 and not up to 125.23 as you would expect. This is appently called Even Number Rounding where any figure that needs to be rounded will be rounded to the nearest even number. The concept is that there will be a 50/50 split of round up to round downs and that they will cancel each other out in the long run.