posgresql query for intervals of 1 min with accumulated sum over all the timeframe

posgresql query for intervals of 1 min with accumulated sum over all the
timeframe

So i'm struggling with this query so far i can create the intervals of 1
min but the sum of the two columns that I need is given for just that min
and not the accumulated sum over time
SELECT
TIMESTAMP WITH TIME ZONE 'epoch' +
INTERVAL '1 second' * round(extract('epoch' from "Timestamp") / 60) * 60
as "Timestamp", SUM("Particles"), sum("Bio")
from "Results"
where "SampleID" = 50
GROUP BY
round(extract('epoch' from "Timestamp") / 60)
ORDER BY "Timestamp" DESC
that is the query that i'm using and the results are these
Timestamp |Sum |Sum
"2013-08-09 14:17:00-07" | 61 | 4
"2013-08-09 14:16:00-07" | 64 | 6
"2013-08-09 14:15:00-07" | 29 | 5
"2013-08-09 14:14:00-07" | 96 | 1
"2013-08-09 14:13:00-07" | 43 | 2
but i need the accumulative sum of those last two colums