Paypal Notification was refused

Greetings,

1. Someone placed an order through my HikaShop. I went to paypal
and the money was successfully placed in my paypal account;
however, I received the following message from paypal:

Hello,
A Paypal notification was refused because the amount received (27.88USD) is different from the order amount (27.87USD)

Check the documentation concerning this issue at www.hikashop.com/index.php?option=com_up...-paypal-error#amount
This notification was for the order 03/04/2013--00085 on the website www.m2820.com/ You can access the order details directly by clicking on the link below after logging in your back end:
www.m2820.com/administrator/index.php?op...ask=edit&order_id=85

2. Also, when I go into HikaShop > Orders to look at their invoice,
HikaShop has two order numbers/invoices for this person and the
"Order Status" for both order numbers/invoices is "Cancelled."

So, why would the amount charged in HikaShop be $27.87, but
then Paypal actually charges them $27.88, then give me this
error message? Also, if paypal actually charges them $27.88,
why does HikaShop show the order is cancelled? How to I fix this?