This is the formal way to say it (although in the case of pounds it would be "12 pee", but more frequent would be: "two twelve" (the dollars/euros and the cents, or pounds and pence, are understood).
"Two twelve" could also be 212 pounds/dollars/euros, say if you are buying a piece oif furniture, but I you are buying only a kilo of tomatoes you woud take it as two dollars/euros/pounds and 12 cents/pence.
Perdón, debía haber puesto "pi". Es decir, en vez de pronunciar la palabra "pence", se dice "pi", sin más (como pis, pero sin la ese al final).
E.g. : 99p (una libra menos un penique) "ninety-nine pi".