If you're trying to convert from a table, try playing with this example:

declare @temp table(thisval float)

insert into @temp values (23.61)

insert into @temp values (1234.13456143)

insert into @temp values (100.00001)

insert into @temp values (12.34)

insert into @temp values (3.14159)

insert into @temp values (10.01)

select cast(thisval as decimal(6,2)) from @temp

Note: if I'm not mistaken (and someone correct me if I'm wrong), it's generally not advisable to put a function into a SELECT statement, since it can use processor time.