Hi Rashmi,
This is more of Non- SAP question however let me try to answer this.
Any ERP system like SAP basically have capabilities to use either methods however in System point of view its the same, these accounting methods are more relevant for Statutory requirements,Auditors and Investors to analyses reasonableness of the reported value of a company's inventory depending on the valuation method used.
RMA-In simple terms retail method is valuated inventory after mark up ( Cost+mark Up) and projected retail inventory ( some retailers)- Sophisticated ERP products like SAP is helping big retailers to help them doing physical inventory based on point of sales and check outs to keep a track of inventory. However it Does not track cost at unit level accurately so true calculation is not performed. Most retail companies are using it avoid cost associated with CMA to track cost accurately at unit level. As per IFRS mandate for all companies using RMA to transform themselves to CMA by 2016
CMA- it uses various methods like FIFO, LIFO or weighted avg price and it value inventory at hand mostly used by manufacturing industry, it helps to accurately track cost at unit level and meets IFRS standards. Cost intensive.
I hope it helps
Best regards
Hrusikesh