The Internal Revenue Service has increased the optional standard mileage rates for the final six months of 2011. Taxpayers can use the optional standard rates to calculate the deductible costs of operating an automobile for business and other purposes. Going up 4.5 cents on July 1, the rate now will be 55.5 cents a mile for all business miles driven through Dec. 31, 2011. The change was made to compensate for increased gas prices.