Please create PO in MRPeasy in the same way as you would create a bill in QuickBooks. If in QBO you do not enter a tax separately, please do not enter it in MRPeasy either.
QuickBooks has localizations with different functions. For example, in the Australian version of QBO, it is possible to configure a tax that is 'Collected on purchases' and 'Purchase tax is reclaimable'. Also, a bill has a separate field for tax. In the US version, this functionality is not available.