Formula to convert 0.976565666 to 0.98

HI All,
I have a calculation where i am calculating a differnece of two % values and would like to return only to one decimal place . For example 1-.22 =0.78 . I need to only show upto 0.7. I know I can handle the same in formatting but the reason I need to change the value itself is that I need to use it in a report filter and there, excel is reading the complete value.

Any pointers will help. I tried Round, roundup and rounddown, but i think either they are not helpful since this is diff of % values, so in all cases it is less than 1 or I am doing something wrong.