Rolling Moving Sum issue with Blank Values

KD13 

I have recently solved a similar issue
Mine was based on years instead. 

Solution I used: 
1. Created a new table containing all years
2. Connected this table to the main one with a join on the year
3. Created a Running total from PBI quick measures using the Years column in the new table (so Base Value= [Value you want to show cumulative/running total] & Field = [Years from new column])
4. Make sure to place your Years/Months column from the NEW table on the chart or table you want to show
worked like a charm!

Edit: PowerBI will show blank if there are no sales/profit/value in a certain time period, which is very frustrating thinking that logically, it should carry the previous value as you stated in your post.