You need a developer to extend the EDT, this changes that referenced EDT everywhere. Lots of debate here, simple change that Microsoft recommend you parallel test for 6 months to validate it does what you want, because there is code that will not reference the EDT but round anyway during the calculation etc. Simple change, huge consequences as the cost is everywhere.
Right click on field and click setup( if you use ax 2012 right click and personilize) and than find the feld and open field properties and change decimal value and save .