how to round 2.2875 to 2.29

There's 2 issues here:

1. you haven't defined the decimal with any precision, so by default is defined as decimal(18,0). When you asign 2.2875 to it, it essentially rounds it, giving 2

2. the second parameter of the round function is the number of decimal places to round to.

so your code needs to be

declare @d decimal (8,2)  --for example  
set @d='2.2875'   
select round(@d,2)

gives

2.29