I created a small test database, with two tables: tblSales and tblCustomer. tblSales was as your example, with a second company, COMPANYSTU, with sales over the period < 60,000. First, I rewrote your query to get a similar join.

Code:
SELECT [tblSales].[Posting Year],
 [tblSales].[Cust Nbr],
 [tblCustomer].[Cust Name] AS [Cust Name],
 [tblSales].Sales
FROM [tblSales] INNER JOIN [tblCustomer]
 ON [tblSales].[Cust Nbr] = [tblCustomer].No_;
Then, I used those results to calculate the sum over the period, then grouped by Cust Nbr.

Code:
SELECT  SUM(A.Sales), A.[Cust Nbr] FROM (SELECT [tblSales].[Posting Year],
 [tblSales].[Cust Nbr],
 [tblCustomer].[Cust Name] AS [Cust Name],
 [tblSales].Sales
FROM [tblSales] INNER JOIN [tblCustomer]
 ON [tblSales].[Cust Nbr] = [tblCustomer].No_) as A
GROUP BY A.[Cust Nbr]
HAVING SUM(A.Sales) >60000 
;
I then saved that the above query as Query2, and created another, Query 3, to join back to tblCustomer to get the names. I used the Design View for this step (Note my earlier suggestion, build step by step with Design View, then copy and paste into the criteria fields). The calculated sql was:

Code:
SELECT tblCustomer.[Cust Name], Query2.Expr1000
FROM Query2 INNER JOIN tblCustomer ON Query2.[Cust Nbr] = tblCustomer.No_;