A joint between wall tiles and a worktop without grout will not look very nice and will trap dirt/germs. Use tile spacers below the tiles to give a small gap for grouting once the adhesive is set. You could also add a silicone caulk after that to make the joint totally waterproof but it's a matter of personal choice and as it would be the last part of the job you will be able to see how it looks without it before deciding.
