Looks like there is some IBM token ring mux units hung from under the center of the first picture. Its too bad that your client will not let you remove that to reduce the clutter. I can almost guarantee they won't be installing cash registers using that wiring system.
Probably at the bottom of this mess is some coax or twinax cable from the first generation of IBM cash registers depending on how old the store is.
On the plus side if your being paid by the hour to sift through this mess, its better than working in a hot attic.
