You (or the purchaser or transferee) must complete Form CBS-1, Notice of Sale, Purchase, or Transfer of Business Assets. Form CBS-1 must be filed with IDOR at least ten (10) business days prior to the date of sale or transfer.Currently, combined sales tax rates in Illinois range from 6.25 percent to 11 percent, depending on the location of the sale. This comprehensive guide explores the complexities of Illinois small business tax. I am going to show you how to fill out sales and use tax form st1 for illinois sales tax.