If you should be charging sales tax but aren't, you could be breaking the law. Most physical products, and some services require sales tax to be charged.
When I first started out, this was a totally foreign area, and I had no idea what was what. Let me give you a quick crash course on sales and use tax.
First off, you have to have a Sales and Use Tax permit in order to charge sales tax. You can obtain this easily through your State Comptroller.
Sales tax is paid in two parts: to the state and to the county. The State Comptroller will make sure both parties are paid when you pay your sales tax.
So how does this whole sales tax thing work? Basically, you get your license, and start applying sales tax to your taxable products and services (we'll get to that below). Let's say you have an online store, and you charge sales tax. Item A sells for $10.00, so you collect (in Texas) $10.81. The entire $10.81 goes to you. The merchant that does your payment processing doesn't do anything but collect the funds for you.
Sales Tax is collected every quarter- every 3 months:
For sales in
January- February- March Sales tax is due in April
April- May- June Sales tax is due in July
July- August- September Sales tax is due in October
October- November- December Sales tax is due in January
This means that you have to SAVE the sales tax that you have collected for those full three months to pay to your State Comptroller. If for any reason you spend the sales tax you collect, you'll have to replace it when it's due out of pocket. The State Comptroller will send you a reminder that your sales tax is due in 10 days (may vary from state to state).
When you're ready to pay your sales tax, you log into your State Comptroller account, and you simply plug in the dollar amount of taxable sales.
You'll also be required to pay tax on items that you purchased for your business tax free. This is where the "use" of Sales and Use Tax applies.
The Comptroller system will calculate the amount of sales and use tax you owe based on the amount of sales you enter. Don't be tempted to fudge the numbers because your payment processing merchant is also reporting the amount of sales you're making, and the State Comptroller WILL find out. This has never happened to me, but don't think that you'll get away with lying.
If you pay your sales tax late, you'll be charged a nice little late fee. This has happened to me at least twice because I totally forgot. It was about $50 a pop. If you overpay, they'll typically reimburse you.