Tax calculation not adding correctly

Tax calculation not adding correctly

I'm having a problem with my taxes on invoices. Currently I have two taxes set up; PST at 7.0% and GST at 5.0%. I've set them up as a group so that they display separately however when the two are added together as a group they add up to 12.35% for some reason. This means that I'm constantly overcharging taxes. I checked both rates a reset them to 7.0 and 5.0 respectively but it hasn't changed the group rate. I need to get this fixed soon. Can anyone help me with this?