The article investigates the theoretical and methodological principles of the mechanism of using RRO and PRRO in terms of increasing the level of tax administration. A three-level system of legal regulation of the use of registrars of transactions in the activities of economic entities has been formed and analyzed. The general tendency of development of cash registers in Ukraine, which consists in gradual, starting from 2015, fiscalization of settlement operations of small business representatives - legal entities and natural persons- entrepreneurs on a simplified taxation system, is highlighted. It was found that the main prerequisite for the process of fiscalization of settlement operations in Ukraine was too high level of the shadow economy, which leads to a shortfall in a significant share of budget revenues. The goal of fiscalization of settlement operations, which is to reduce the level of the shadow economy and protect consumer rights, has been determined. The position on the need to use cash registers when receiving payments through online banking using mobile applications, when receiving payments on a key card and in the case of receiving payment for goods sold through a payment intermediary Nova ay is substantiated. The classification and comparative characteristics of registrars of settlement operations with the definition of the advantages and disadvantages of classical and software RRO in order to facilitate the adoption of quality management decisions when choosing the type of cash registers.