COUPONS off by a cent or more when passed to PayPal or eway.

-- HikaShop version -- : 3.4.0
-- Joomla version -- : 3.8.8
-- PHP version -- : 7.0
-- Browser(s) name and version -- : firefox 60.0.2

Please help, I need to get COUPONS to work properly, but it doesn't always pass the correct amounts to PayPal or eway.

For example, I have setup a COUPON called TESTING99 that has a value of 99.950%, and when I checkout and apply the coupon, the discounted amount in the checkout cart is correct, but when passed to PayPal, it is off by 1 cent, so it becomes an invalid order "A Paypal notification was refused because the amount received (0.30AUD) is different from the order amount (0.31AUD)". In the admin panel - the My Frequency Store Orders it shows $ AUD0.31, even though the checkout cart showed "$ AUD0.30", and the amount passed to PayPal shows "$ AUD0.30".

The store is in Australian currency, and has both the USD and AUD displayed and published. The default currency is AUD.

The product I was testing with was I added a product to checkout called:
Activate Your Personal Quantum Shift - Parts 1 & 2, by Qala - $ AUD250.00 and
Experience Your Loving Presence - LEVELS 1, 2 & 3, by Qala - $ AUD360.00

I applied the coupon TESTING99, selected PayPal, accepted the terms, the cart is recalculated automatically:
Subtotal $ AUD610.00
Coupon $ AUD-609.70
Total $ AUD0.30

$0.30 AUD is the total that appears on PayPal, but the Summary of the Order email shows a slight more:
Subtotal $ AUD610.00
Coupon $ AUD-609.70
Total $ AUD0.31

On the backend on the My Frequency Store Orders, it shows $ AUD0.31. If I submit the order and pay using PayPal checkout, the order is not accepted by hikastore, the administrator gets this message: A Paypal notification was refused because the amount received (0.30AUD) is different from the order amount (0.31AUD)

We have had inconsistent results with Eway checkout as well.

Some products with different prices, works, for example: the product The Energy Science of Your Universal Connection, by Qala for $ AUD1,100.00, works correctly all the way through. No issue with this product price.
Subtotal $ AUD1,100.00
Coupon $ AUD-1,099.45
Total $ AUD0.55
This product has no pricing inconsistency, so the checkout for this product works.

Thank you Philip, #2 below seemed to do the trick - when "Send details of the order" is set to No - as it works properly now; I already had Round prices during calculations set to No.

Thanks again for your help.