There are two meanings of ‘till’. One is to till or tend the ground, and while that is a less potent image nowadays, the image still appears in dreams in the sense of cultivating opportunities.
The other meaning is as a safe, temporary repository for money.
It is this symbolism of a commercial transaction which is the one most understood.
In dreams, a broken cash register would symbolize the breakdown of our ability to accumulate resources and also possibly signify debt.