Formula language uses wrong rounding (aka account rounding or banker's rounding), LS uses correct rounding (aka scientific rounding. Damien Katz approves the difference in his comment on this blog.
Seriously, there is no wrong rounding (or rather: no right rounding), it's all a matter of definition. I can see the rationale behind accounting rounding, but still think it's a really bad idea. Even worse to have different rounding algorithms implemented in different languages in the same software product.