Collecting Sales Tax
If you sell products, you probably will have to deal with sales tax. In fact, even if you provide only services to your customers, you may still have to deal with sales tax, although that's still more the exception than the rule. Either way, sales tax tends to be pretty straightforward: you collect it from customers, then send it in to the state along with a brief sales tax return.
From an accounting perspective, the sales tax that you get from customers has nothing to do with revenues, and the sales tax that you pay to the state has nothing to do with expenses. Yes, you collect sales tax as part of a sales transaction, but that part of the transaction has absolutely no impact on your statement of profit and loss. Instead, this is a balance-sheet-only transaction affecting two accounts: sales tax payable and cash. At the time of sale, you debit the cash account and credit sales tax payable as part of the overall sales transaction; when you send in the payment, you debit sales tax payable and credit cash, just as you would for any other payable account.
Whether sales tax comes into play is a state issue. You can learn about your company's specific sales tax requirements by contacting your state's revenue collection office. There you will find out which items are subject to sales tax, how much tax you have to collect, which form you have to fill out, and when you have to send it in (along with the cash you've collected).
In some cases, though, you may not have to deal with sales taxes at all, no matter what you're selling. The most common reason for this is called the resale exemption. That means if you are selling products to someone who is going to resell them to someone else, you don't have to deal with sales tax; only the company that sells the product to the end user does. To cover your company, make sure to get resale certificates from your customers; state sales tax authorities often check up on this.