The tax bill for the average single-family home will increase approximately $110 in fiscal 2013, a figure in line with Mayor Thomas Koch’s proposals. According to city officials, the increase continues a several-year trend of keeping homeowner increases well below state averages, while maintaining one of the largest excess levy capacities in the Commonwealth. Although residential tax bills have been curbed, the city’s businesses, which are taxed at a higher rate, say they are feeling the burden. “Though times are challenging . . . we hear it from commercial taxpayers how expensive it is in the city,’’ said Dean Rizzo, president of the Quincy Chamber of Commerce. “We want to be cognizant of that and . . . try to offer the most favorable rate we can while keeping the city fiscally strong and vibrant.” Commercial properties are taxed at a rate almost double that of the residential properties.