How to return 0 if now rows in query?

This following block of SQL does a calculation:
UPDATE labordata SET rmrtotal = t1.sumtotal FROM labordata INNER JOIN
(SELECT IsNull(SUM((((labordata.cost * labordata.qty) * (mbillcode.rmrperc / 100.0)) * (1 - (mbillcode.discper / 100)))),0) as sumtotal,
labordata.sanum,labordata.jobnum,labordata.altnum,labordata.docid,labordata.laborid,mbillcode.onfield,mbillcode.fixed
FROM mbillcode INNER JOIN labordata ON
labordata.sanum = mbillcode.sanum AND labordata.jobnum = mbillcode.jobnum AND labordata.altnum = mbillcode.altnum AND labordata.docid = mbillcode.docid
AND labordata.fldr = 'none' and labordata.laborid = mbillcode.laborid
WHERE mbillcode.sanum = @sanum and mbillcode.jobnum = @jobnum and mbillcode.altnum = @altnum and mbillcode.docid = @docid AND mbillcode.onfield = 'Labor Hours Cost' AND mbillcode.fixed = 0
GROUP BY labordata.sanum,labordata.jobnum,labordata.altnum,labordata.docid,labordata.laborid,mbillcode.onfield,mbillcode.fixed)
t1 ON t1.sanum = labordata.sanum AND t1.jobnum = labordata.jobnum AND t1.altnum = labordata.altnum  AND t1.docid = labordata.docid
WHERE labordata.sanum = @sanum AND labordata.jobnum = @jobnum AND labordata.altnum = @altnum AND labordata.docid = @docid AND labordata.laborid = t1.laborid AND t1.onfield = 'Labor Hours Cost' AND t1.fixed = 0 and labordata.fldr = 'none'

If there are no rows returned from the joins, I need sumtotal to = 0. I was thinking to do an IF @@ROWCOUNT after but maybe there is a better way?

IF @@ROWCOUNT = 0 SET etc etc....

Thanks.