So, I ran across a problem with QuickBooks that involves some of the most basic math that we were all taught in elementary school: how to round numbers properly. You’d think that a company that makes accounting and invoicing software for a living would understand how rounding of numbers works. But based on the last hour of having to edit the data that gets send to QuickBooks from our internal system you’d be wrong.
Denny’s example is $3.18497736 and rounding happens after four decimal spots, so it’s $3.1849 or $3.1850. Denny expects $3.1850 and QuickBooks gives $3.1849.
In this case, Denny’s right. The part that confuses people is banker’s rounding, which has you round to the even number if your last digit is a 5. For example, if it were $3.18495 and you round to four spots after the decimal, that would be $3.1850. With $3.18485, it would round to $3.1848.
.NET uses banker’s rounding by default, which can confuse people unfamiliar with the concept. SQL Server, meanwhile, rounds the way that Denny expects: 5 or higher rounds up, 0-4 rounds down.