V speeds: If there is only 1 knot in it, who cares which way you go?
But if you have several knots spread, it depends.....
Personal preference is to round up for take-off. Two reasons. 1: I would rather be on the ground than in the air if it is going pear-shaped approaching V1 and, 2: a higher V2 speed provides more margin over Vmca and often a better climb.
Exception to that would be on a limiting or wet/slippery runway, when rounding V1 down makes sense, subject to being within the allowable envelope.
For landing I tend to always round down, e.g. if the landing charts are in 500 kg increments and estimated landing weight is mid point, I will go to the lesser numbers. Given that Vref is 30% above stall speed there is enough margin that if, for example, rounding down resulted in 25% it would still be within an acceptable range for most transport types. Using FMS the numbers are usually more exact, so I would use whatever it gave me, but ignore any decimal points!
Others may disagree and there may be some types that do not handle well right on Vref. Also, I have seen ops manual instructions to always round up. So be it; follow company policy if stated.
Last edited by Mach E Avelli; 11th Dec 2012 at 07:59.