FLOOR Function (DAX)
Rounds a number down, toward zero, to the nearest multiple of significance.
If either argument is nonnumeric, FLOOR returns #VALUE! error value.
If number and significance have different signs, FLOOR returns the #NUM! error value.
Regardless of the sign of the number, a value is rounded down when adjusted away from zero. If the number is an exact multiple of significance, no rounding occurs.
The following formula takes the values in the [Total Product Cost] column from the table, InternetSales.and rounds down to the nearest multiple of .1.
=FLOOR(InternetSales[Total Product Cost],.5)
The following table shows the expected results for some sample values.