how u are assigning the data to crystal table?
i think if u are having data table then in that table it self u can write the logic in such way that it carries the value of previous row and add it into next row.
something like this
select a.somcolmn1, a.somcolmn2, sum(b.somcolmn) as price
from TableName a cross join Sametable b
where b.Id <= a.Id
group by a.Id, a.somecolmn
then assign the entire table to crystal row