When rolling, you will roll for the duration of the note and release (tap) on the tied note.
In a regular untied note (without a roll), the value of the tied note(s) are added to the first note. Since the drum is stacatto, you attack the first note and hold (count) the note that it is tied to. In an instrument that sustains sound, such as a trumpet, the first note is attacked and sustained to include the value of the tied note.
Pick up Primary Handbook for Snare Drum by Garwood Whaley. There are tied examples in there. There is also an accompanying CD so you can hear how it should be played.
Jeff