Calculate using custom defined decimal places

Hi,

I have a calculation which produces X, Y and Z.

The values have two decimal places, but I only want to display up to 1 decimal place.

e.g. X = 2.41, but I will display 2.4
Y = 2.55, but I will display 2.6

I want to display Z as a difference between X and Y ... and I want to calculate Z after the rounding of X and Y
e.g. I want to display as [2.6 - 2.4 = 0.2], but not [2.55 - 2.41 = 0.1]

Where do I make this change to reflect this ?

Thanks in advance.