MySQL: Is there a performance hit comparing numbers with an important precision -

i'm wondering in mysql if better performance compare numbers important precision or round them before comparing, knowing comparison precision less important compared numbers precision.

ex:

select 0.123456789101112123456789101112 < 0.987654321012345987654321012345   

or

select round(0.123456789101112123456789101112,2) < round(0.987654321012345987654321012345,2) 

there's performance hit in version uses round().

first, calling function more expensive not calling function.

second, , possibly more significantly, if there's index on column, can't used if perform function on column before comparing something.

but getting right answer practically more important using efficient method.