Using Math.round to round to one decimal place?

I have these two variables

double num = 540.512
double sum = 1978.8

Then I did this expression

double total = Math.round((num/ sum * 100) * 10) / 10;

but I end up with 27.0.

In fact I have many other variables and when I use them in the expression I always get a 0 in the tenth’s place.