The currency is the pound, not the penny. It would be daft to think the basis of comparison was the penny and it would also be daft to lose money on each transaction because you couldn't receive all the change owed you, something more likely to happen when you have less factors available due to less subdivisions and/or a different choice of base.

It's also not going to matter only at the point a dozen eggs is a pound, but this is well off the original point and I'm not interested in a position that, strangely enough, means decimalisation has no impact. 240 pennies is 240 pennies, after all.