Means "money" is to, or can be, made in an
instant.
References
the sound older type cash registers made when tabulating a final bill.
Like when someone slips and falls on a banana peel in
Trump Tower due to the
negligence of the
Trump Tower clean up crew to remove that discarded banana peel from its entrance way. That first thought in one's mind would be LAWSUIT!! ...and the first words out of their mouth would be "CHA' CHING"