Problem With Round Function In TSQL

Trying below instructions

create table t

(


indexvalue float

)
go

insert t

values (109.1)

insert t

values (109.3)

insert t

values (109.5)

insert t

values (109.9)

go
select *

from t


select sum (indexvalue) / count (*)

from t


select round (sum(indexvalue)/count (*), 1) -- this line is result of round (109.45) shows 109.4 that is incorrect
from t --why round function doesn't work correctly in this select


select round (109.45, 1) -- but this line results 109.5 that is correct