This is the screen you see when you edit a customer group. In the first box titled Personal you can choose whether to show prices with tax included and also if you want to exempt a group from being charged tax. Displaying prices with tax included is primarily used for European sites where this is required by law. In the box titled Exempt Group from Specific Tax Rates you can tick specific taxes the group is exempt for. This has no effect if you made the group Tax Exempt.