See the commit that added round_away_from_zero for details. IN the case of dashboard_data.py: We don't first cast to decimal here because in python 2 this didn't do anything. The python 2 rounding method would just cast things to float before doing the rounding anyway so it just wastes cpu cycles. In python 3 this causes some typing issues so just removing it.
common ------ This directory contains common code shared between LMS and CMS, such as Mako templates, CSS, and Coffescript.