I have the same problem ... different PayPal calculations!
I realize that only when put products on sale.
I don`t use decimals because use round prices.
Normal Product Price: 189
On sale 50% - product Price: 94,50 - Rounding in Prestashop - Total to pay: 95
I get error because PayPal calculate: 94,50
In my case when i set Number of decimals: 2
it resolve error problem but then ugly total amount is with decimals ...
PS 1.6.1.6
PayPal 3.11.1