It would be better to target the companies which make their PoS and self check out systems. If those systems dont support it, then the grocery store will likely never accept it due to the overhead of manually processing a transaction. This also has the upside of having other retailers which use those PoS systems, being able to accept bitcoin.
I agree, the infrastructure needs to exist first to allow retailers and grocers to quickly and seamlessly transact with Bitcoin. And the best place to get that done is through the Point of Sale systems used.
As it stands now, it's only "convenient" for smaller businesses because the amount of overhaul that has to be done is fairly minimal when compared to all the Logistics of rolling it out in retail.