I've done 4 or 5 before but it has been a while. I seem to recall a post by Frequent Miler where he did like 15 or something outrageous.
However, if you're buying merchandise, you could always just buy yourself $120 Lowe's gift cards in separate transactions. Then use the Lowe's gift cards together to get whatever you need.
Even better, you might want to use the gift cards to make the purchase online if you can. I've had good luck in getting rebate portals (topcashback mostly) to payout when paying with Lowe's gift cards. But note there is a limit of 5 when using gift cards online to pay.
And finally, I ALWAYS purchase a coupon on Quik Coupons to use at Lowe's. You can typically find one for 10% off for bigger purchases or $20 off $100 for smaller purchases (but note the expiration date on these).