Percentages are what the bookmaker builds into their prices in order to make a profit.
Fortunately for the punter different companies often have different odds for the same events, giving us the chance to shop around for the best value. The best price percentage tables show the relative value for the customer - the lower the percentage, the more value to the punter. There are a number of tax free options available to punters these days, most notably with online bookmakers. Many offer tax free betting or tax at a reduced rate. By shopping around on the internet you can find the best deal for yourself.