MERGE a UNION query results down to one row per KEY value
It seems you just need to use a derived table or common table expression with a new grouping level:

DECLARE 
    @FROM datetime = CONVERT(datetime, '12-30-2013 03:00:00', 101), 
    @TO datetime = CONVERT(datetime, '12-28-2014 03:00:00', 101);

WITH Combined AS
(
    SELECT 
        DivisionName = d.DivisionName, 
        [CC w/o Tips] = (SUM(PaymentAmount) - SUM(TipAmount)), 
        [Tips] = SUM(TipAmount),
        [Receipts] = SUM(PaymentAmount)
    FROM LFLive.POS.OrderPayments AS op
    JOIN LFLive.POS.Orders AS o
        ON o.OrderId=op.OrderId
    JOIN LFLive.POS.Payments AS p
        ON p.PaymentId=op.PaymentId 
    JOIN LFLive.Directory.Divisions AS d 
        ON d.DivisionId=o.DivisionId  
    WHERE 
        op.IsVoided=0 
        AND op.IsDeleted=0 
        AND o.IsVoided=0 
        AND o.IsClosed=1
        AND o.OrderTypeId = 2 
        AND p.PaymentTypeId = 6 
        AND o.DateClosed BETWEEN @FROM AND @TO
    GROUP BY 
        d.DivisionName

    UNION ALL -- Not UNION!

    SELECT 
        DivisionName = d.DivisionName, 
        [CC w/o Tips] = (SUM(PaymentAmount) - SUM(TipAmount)), 
        [Tips] = SUM(TipAmount),
        [Receipts] = SUM(PaymentAmount)
    FROM LFArchive.POS.OrderPayments AS op
    JOIN LFArchive.POS.Orders AS o
        ON o.OrderId=op.OrderId
    JOIN LFLive.POS.Payments AS p
        ON p.PaymentId=op.PaymentId 
    JOIN LFLive.Directory.Divisions AS d 
        ON d.DivisionId=o.DivisionId  
    WHERE 
        op.IsVoided=0 
        AND op.IsDeleted=0 
        AND o.IsVoided=0 
        AND o.IsClosed=1
        AND o.OrderTypeId = 2 
        AND p.PaymentTypeId = 6 
        AND o.DateClosed BETWEEN @FROM AND @TO
    GROUP BY 
        d.DivisionName
)
SELECT
    C.DivisionName,
    [CC w/o Tips] = SUM(C.[CC w/o Tips]),
    [Tips] = SUM(C.Tips),
    [Receipts] = SUM(C.Receipts)
FROM Combined AS C
GROUP BY
    C.DivisionName
ORDER BY 
    C.DivisionName;


I replaced the UNION with UNION ALL because you don't want duplicate removal.