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These terminals do not allow you to override the tax tables inside the register
It has been a long time since these tax tables have been updated. Yu may be able to use a combination of two taxes which add up to what you need. I know it is not an elegant solution, but it might be a workaround to the problem. If you do have a POS dealer, they may be able to apply an update to update the tables, but I'm not even sure if that is available to them.