You (or the purchaser or transferee) must complete Form CBS-1, Notice of Sale, Purchase, or Transfer of Business Assets. 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. When selling a business in Illinois, common tax implications include capital gains tax on the sale of business assets and potential state taxes. This blog provides instructions on how to file and pay sales tax in Illinois using form ST1. Assets" form (CBS-1).