Using AvaTax, why are the Tax on Transactions with discounts changing when importing to NetSuite?

We use Avalara avatax in netsuite as well as in our webstore on the bigcommerce platform. The customer orders their product; tax is calculated using avatax; customer pays. Order is them imported into netsuite with script. All orders that have sales tax and a discount are off by a penny. It used to be more because we used item groups in netsuite but I changed those to kits/packages so the price was independent of the components. I have spoken to Netsuite who says it's avalara issue, Avalara said its netsuite in how they calculate tax,