Yes, if they were both numeric(9,2) then there should not have been any rounding. If either value were real instead of numeric(9,2), then the result would make sense, because the precision of real is only 7 digits.

To wit:

DECLARE @firstNumeric NUMERIC(9,2)=1676559.81

DECLARE @secondNumeric NUMERIC(9,2)

DECLARE @real REAL

SELECT ISNULL(@firstNumeric,0)+ISNULL(@secondNumeric,0)

SELECT ISNULL(@firstNumeric,0)+ISNULL(@REAL,0)

Are you absolutely certain both values were numeric(9,2)?

Cheers!