Buy 3 robitussin, get back 10.00 RR,

Buy 2 listerine for 11.00 and use the 10.00 RR and get back 6.00 RR,

Buy 1 crest pro health (plus some fillers) and use the 6.00 RR and end up with 4.29 in RR.

Would there be any glitches in getting the RR if I do the above plan?

There shouldn't be. Good plan!

Looks good!
shouldn't have any issues as you are not using same rr's to pay for same items!

that's exactly what I did yesterday.

(store #1)
1. buy 3 robitussin, get $10RR
2. spent that $10rr on 2 listerine and get $6 RR

(store #2)
3. spent $6RR on 3 more robitussin + stuff, get another $10RR
4. spent $10RR on 2 more listerine, get yet another $6RR

(store #3)
5. spent $6RR on crest rinse and excedrin (rebate #1), get $4.50RR
6. spent $4.5RR on last 3 robitussin, get $10RR

at this point, i have drown myself in cough syrup and mouth wash, so I decide to end my shopping spree and plan to spend my last $10RR on other rebate items.