When I adding Item first time in the cart I facing Issue in calculation of subtotal and Total (incl. BTW) why?

I am currently working on magento 2 Website .I facing one issue IN Site, While I am adding item first time in the cart in Total (incl. BTW) price and subtotal gives different value.

Subtotal $ 795,00 Total (excl. BTW) $ 663,22 BTW $ 139,28 Total (incl. BTW) $ 802,50

And When I Update Quantity in Cart price of subtotal and Total (incl. BTW) gives same and correct value. Subtotal $ 1.590,00 Total (excl. BTW) $ 1.314,05 BTW $ 275,95 Total (incl. BTW) $ 1.590,00

Can Anyone Help Me For solve this issue?