I really don't understand why this correspondence has got this far. Of course a pharmacist's assistant who refuses to sell contraceptives for religious reasons is imposing that religiosity on the customer. Saying that the customer can go elsewhere is merely dodging the issue - using a practicality to get round the principle.
Supposing there wasn't an 'elsewhere'. Would the assistant still be entitled to refuse to serve the customer? If so, then the customer would be refused contraception because of someone else's religious beliefs. If not, then the assistant would have to hand the item over regardless of her beliefs, so why can't she do that anyway?
It has been said by others before me: that no-one should take a job (pharmacist's assistant, check-out employee, adoption arranger) where their religious beliefs are going to affect other people adversely - just as I, an atheist, would not take a job where I had to promote beliefs I disapproved of.
(Come to think of it, I was once in that position when I was approached by an Order of nuns to make a film about them. I pointed out that I was an atheist and was therefore not prepared to promote their religious beliefs in any way. They said that was fine by them. So I made a film which told of how Blessed Julie of Namur (as she was then - has she been canonised yet?) founded the Order to give an education to poor children, work which the Order still carried out in poor districts, especially in my home city of Liverpool. That work was so worthy that it stood out on its own without the need for me to justify it on religious grounds. The final film pleased them and left my conscience unworried.)