Nowadays, the market demand for web applications is increasing mainly due to the rapid development of the Internet and numerous web technologies. By applying the newly developed technologies multimedia applications are being created daily, granting the users access at any moment via ''smart'' devices. One such application is the fiscal cash register ''Fiskali'', which adapts to all screen dimensions, ranging from the smallest mobile screens up to large format computer monitors. The topic of this thesis is the development of the web application ''Fiskali'', a fiscal cash register that operates in accordance with Croatian fiscalization laws. By using the application the user manages company data, business branches, payment terminals, employees, buyers and product items. The main advantage of the product being a web application is that it can be accessed online, therefore it isn't necessary to have it installed on the client computer. This thesis describes in detail the technologies used as well as the performance of the system via diagrams and application operating instructions.