Rounding fix for Mijireh tax ex. price

As committed on master branch:
- https://github.com/woothemes/woocommerce/commit/02c754b6746e69112d9ee24f509d271f5a182357
- https://github.com/woothemes/woocommerce/commit/db95f1e772656b64b1be9f19364ff18392389beb