T-SQL (SS2K8) :: Matching Two Data Sets

I have two tables - one with sales and another with payments against those. The payment may not match the exact amount of sales and I have to use FIFO method to apply payments. The payment month must >= sales month.

How can i write a query to do this? Examples are as below.

Table 1
Sales Sale DateSale Amt
1Jun-141200
2Oct-142400
3Dec-14600
4Feb-1512000

Table 2
Pay Month Pay YearPay Amount
5 2014 300
6 2014 1000
10 2014 500
11 2014 2000
12 2014 300
1 2015 900

create table tbl1
(
saleNo int
,saleDate date
,saleAmt float
)
insert into tbl1 (saleNo, saleDate, saleAmt)

[Code] ....