Your cash register is your main book of entry. In many businesses, the cash register actually consists of two separate registers, your Cash Disbursements Register (where you record all your payments) and your Cash Receipts Register (where you record all your deposits). In other businesses, the cash register is the same as your cash disbursements register and the cash receipts register is kept separate.
However, in many computerized and manual accounting systems these two registers (cash disbursements & cash receipts registers) are combined into one book of entry called the "Cash Register".
As you have probably figured out by now, once combined this "Cash Register", is very similiar to a checkbook, which lists the payments & receipts from/into the business bank account.
When the two registers are combined into one, in a manual system, the common format is to list receipts on one page (cash receipts register) & payments another (cash disbursements register), totaling each monthly. The total should be broken out into sales tax (if applicable) & the net (the amount after deducting sales tax) receipt or payment by type (purchases or telephone, etc.).
You may want to download a free cash disbursements register and cash receipts register, to have a closer look.