Fixing Calculation Issue

Hi We had a freelancer on here build a Magento e-Commerce website, their is some complexing pricing functionality which goes on and the freelancer on here which did the website did not finish it properly so it mis-calculates some figures. The website is a Ribbon e-Commerce store and is currently live, the way the calculations are supposed to take place are: - If a user orders under 5 rolls a 10% surcharge is added - The client has the ability to put users on to specific 'Price Bands' these are 5%, 10%, 15%, 25% and 35%, so if a user is put on a 35% price band, they pay the default price + 35% What the client is saying, is that the 10% surcharge is not working correctly if a user orders under 5 rolls. So we need someone to fix this issue. Only qualified persons please apply for this project, we don't want another freelancer who is incapable of doing the job properly. Thank you