I am having trouble calculating the 6 month rolling total with SQL of this table 

I've got in Table.1 something like this 

Customer Name | Month of Sale | Revenue in the Month 

X Co | Jan 2016 | $5,000

X Co | Feb 2016 | $4,000

Y Co | Jan 2016 | $8,000

Y Co | Mar 2016 | $1,000

Z Co | Dec 2015 | $800

Z Co | Feb 2016 | $2,800

.....

.....

.....

I want to create a table that looks like: 

Month of Sale | Last 6 Months Rolling Revenue

Dec 2015 | $x

Jan 2016 | $x

Feb 2016 | $x 

Mar 2016 | $x

In this table, the Dec 2015 6 month rolling revenue will be:

Jul 2015 + Aug 2015 Rev + Sep 2015 Rev + Oct 2015 ... + Dec 2015

Thanks