Small Business Tax Relief and Job Growth Act of 2010 - Amends the Internal Revenue Code to: (1) increase the tax deduction for business start-up expenditures; (2) allow expensing in 2010 and 2011 of improvements to real property and structural improvements to buildings used in a trade or business; and (3) reduce from 35% to 15% the alternative tax on the net capital gains of C corporations with annual gross receipts of not more than $15 million.