The issue is that you need to add each value, one at a time, and evaluate that. You cannot add them all up at once, and then apply rounding.
Look at this example:
1.2+1.2+1.2+1.2+1.2
If you add those up, you get 6.0. There is rounding to be applied, but that is not the correct answer for you. You are expecting 6.4.
So, what you are working with is data whose data whose format does not really represent what it is. I cannot think of any easy solution around this. If it were up to me, I would do one of two things:
1. Fix the data, so the entries are actually times and not numbers. If this is the way the data comes over and you have no control over that, I would create a macro to either fix it as they are entered or all at once.
2. Create my own Function in VBA that does special adding, where it goes through each entry, one at a time, and make the proper adjustments.
We can help you do either of those two things.