It's used to represent:
* The sound of money being deposited into a cash register.
* The act of making money, especially quickly or easily.
* The feeling of excitement or satisfaction when money is received.
For example:
* "I sold my old car for £1000! Kerching!"
* "She's been kerchinging it up at the casino lately."
* "The sound of the cash register kerchinging is music to my ears."
It's a playful and informal word, often used in a humorous context.