PayPal Express Error 10426

I've searched all over the web and haven't found the answer to this. I'm desperate!

I just upgraded from 1.5.1 to 1.5.4 because of this error and still have the same problem.

It seems to happen only on discounted items. I don't think it has anything to do with sales tax because customers from all over the country seem to be getting this error.

PayPal seems to calculate things in correctly because I see different totals on the PayPal checkout screen than the actual order.

I looked at the logs and it looks like there is also an error 10413, which may occur before the 10426 error.

I tried editing the thread but couldn't.
This seems to only be a problem when someone orders 0.5 units?

This?

https://www.zen-cart.com/showthread.php?218231-PP-EC-errors-10413-and-10426-same-sale&highlight=10426

Yes.

I made the changes suggested here: https://github.com/zencart/zencart/pull/500/files and it seemed to fix the issue.
Wasn't sure whether those would work on 1.5.4 but so far so good.

Thanks!