Используйте trunc
вместо округления, как @a_horse_with_no_name, предложенное в комментариях
with tbl as (
select 16.49 price, 1460 quantity from dual union all
select 16.4991, 1460 from dual union all
select 15.63, 38638 from dual union all
select 15.6352, 38638 from dual
)
select trunc(price, 2), quantity, count(*)
from tbl
group by trunc(price, 2), quantity