First off, instead of using DT_DECIMAL, I'd recommend using DT_NUMERIC. Since you're dividing by 100, I assume you're looking for a value with two decimal places. This will allow you to specify your precision.

Second, you could change your task to this instead, which would allow you to have your output as a number instead of a string:

(DT_NUMERIC,12, 2) ((DT_I1) (sign + "1") * amt) / 100