Checkout

Checkout
 

COuld you pay at the checkout?
could you pay at the (cash) register ?
Could you pay a t the till (BE)?

CAn we use all of them?

I would say that cash register is the actual machine and wouldn't be used in that expression.
I think you'd "go to the checkout" or "pay at the till" (I think this last one, like you point out, is BrE).

In BrE, go to the checkout would always be a supermarket, but any large shop would have a till where you pay. Slight and boring difference. :)

Para mi la palabra "cash" de "cash register" es imprescendible. El sustantivo "register" quiere decir padrón (en el sentido amplio).

No me parece probable que use ninguna de las tres frases que propones. Si alguien me pregunta "You've just bought those? Where did you pay?" es posible que conteste "At the till", pero bueno, es que normalmente no es necesario especificar, se supone que todo el mundo sabe como pagar sus compras en una tienda.

Es decir que las tres son correctas, alguien va a pagar al dependiente y tu dices Could you pay at the till/check-out/cash register?

Estoy de acuerdo con Perikles que "checkout" se usa sólo con respeto a los supermercados.