Bruno Liljefors, 1899, link The tax authority and the tax payer are engaged in an age-old cat and mouse game, tax payers trying to perfect tricks that allow them to pay as little tax as possible and the tax authority trying to close these loopholes. Retail cash payments are one of the fields on which this battle is waged. It's interesting to see how sophisticated this cat and mouse game has become. There are two weak points in the sales process that allow cash-accepting retailers to avoid paying sales taxes or VAT. The first weak point is at the very outset of a payment. When a customer pays with cash, the person behind the till can avoid ringing up the payment. Without a record of the payment having been made, the retailer needn't pay tax. But even if a retailer rings up all cash payments and provides receipts, they can still avoid paying taxes. At the end of the business day, they need only doctor the cash register's data using a zapper —add on hardware or software design