Yes. Once multiple tax refunds from different Ocean partner stores have been confirmed by Customs and added to your Ocean Wallet, you can withdraw them together (some refund methods don't support withdrawing multiple refunds together; in that case, please change your refund method as prompted on the page).
Each purchase's eligibility and refund amount are still calculated separately. The minimum purchase amount is calculated separately for each store on each day, and amounts from different stores cannot be added together.