Nowadays, companies are relying more and more on cause-related marketing (CRM) as an effective corporate social responsibility practice to achieve marketing objectives by consumers’ participation in donations. Specifically, the current study is focused on exploring millennials’ (born between 1980 and 2000) beliefs and understandings of a CRM practice that has received scant attention from marketing scholars despite its effectiveness in raising money: rounding up. For methodological purposes, a structural approach to the theory of social representations is adopted as it facilitates the analysis of interpretations and shared meanings held by a social group about a specific social phenomenon. Thus, drawing on this theoretical approach, the method of free-word associations was chosen and applied to 300 Mexican millennials. Findings indicate that millennials understand the purpose and nature of rounding up and, hence, they are willing to donate money through this practice. However, the mistrust of companies’ practices and intentions by millennials (e.g., tax evasion and misuse of money) affect the credibility of rounding up. Therefore, companies must implement practices to enhance awareness, transparency, and trust in their rounding-up practices.