What does the bold part mean?

•And we can be sure that as long as shock films ring up a merry tune on the cash registers, producers will not desist from making them.


Old-fashioned cash registers had an actual bell that rang when the cash drawer opened. That "chi-ching" has come to symbolize money. Imagine millions of cash registers all over the world ringing and ringing. It would sound like a merry tune to the movie's producers.

P. S. - You "ring up" a sale when you operate a cash register. You ring it up, whether there is a bell or not.

Alice: Here is the blouse I want to buy.

Saleslady: Very good, Madam. Would you like me to ring it up now?

The writer played with that carelessly and funnily, saying that the films ring up a tune, which would be unidiomatic in any other setting.