It's replicating the sound of a cash register/till opening, meaning money (either the prestige of spending or having it). So I would say "Oh, I just got a bonus at work, ka-ching!". In addition it has entered modern English as a positive phrase usually when you are getting something out of something that you didn't expect; "when we arrived at the party there was free champagne, ka-ching!"

Ba-bling - just like a bling bling jewelry that usually worn by rappers like Jay-Z. Cha-ching - is the cash register, money coming in, ker-ching.

urbandictionary.com use the searchbox, you will get all the answers and examples you need. Sorry for not giving exact answer.