Here my examples.
Floor Example: If you have values for instance 12,642,501.91
If you apply floor, it will exclude Decimals no matter
Round Function can have functionality to round the nearest value.
for instance, 12,642,501.91 this will round to 12,642,502 or with round you can apply decimals like below if you want
below example, Round(sum(sales),1) Means, After decimals 1 it will round to nearest highest value. .91 will round to .90
What is your datasource. Floor is not supported function for all sources, so that may be why you have some unexpected results here.
Check your source here for the FLOOR function to see if supported: