The expansion of tax exemptions, incentives, and compliance obligations creates not only revenue effects but also costs for the government, taxpayers, and the public financial oversight system. Some of these costs are not explicitly reflected in budgetary accounts and arise as collection costs, tax compliance costs, litigation costs, administrative resource losses, and revenue foregone resulting from non-collection. This study aims to explain the legal position of the Supreme Audit Court of Iran in identifying, assessing, and reducing such costs. The research adopts a descriptive-analytical method based on documentary analysis of laws, regulations, and legal sources. The findings indicate that the Court's authority to audit revenue and expenditure accounts, examine the legality of financial operations, assess the accurate and timely collection of public revenues, and report on budget execution provides an appropriate basis for supervising tax-related costs. Nevertheless, this oversight must be distinguished from the executive functions of the Iranian National Tax Administration. The study concludes that risk-based oversight, cost-benefit analysis of tax incentives, data exchange, and performance measurement can improve transparency and efficiency in the tax system.