When a rate is a fraction it will be rounded down to the nearest whole number.

Example: if the rate is 5.5:1 and you buy with:

!buy 1 = 5.5 = rounded down to 5 sets

!buy 2 = 11 = 11 sets

!buy 3 = 16.5 = rounded down to 16 sets

!buy 4 = 22 = 22 sets

...and so on.