Sales tax is always collected by a retailer, but not all businesses are required to collect sales tax. Whether you need to obtain a sales tax permit then collect and remit sales depends on something called nexus. Nexus is a connection that creates a sales tax requirement. The most common ways for a business to establish nexus are: Physical presence in a state; Economic activity in a state (economic nexus); Ties to affiliates in a state (affiliate nexus); Referrals from in-state businesses or individuals (click-through nexus). Because economic activity, referrals, and ties to in-state affiliates can establish nexus, businesses based in other states and even other countries can develop an obligation to collect and remit sales tax in states where they make sales. Learn more about sales tax nexus.