Multiple groupings

I've looked at the FAQs, but have had a hard time making any certain methods
work.  I basically have XML that has a PaymentType, City, Date and ID.  I
need to group all records by PaymentType then by City.  I need to total by
city and by Payment type.  Here is some sample XML.

<?xml version="1.0" encoding="UTF-16"?>
<ArrayOfAccountLineItems>
        <AccountLineItem>
                <ID>12993</ID>
                <PaymentType>Credit Card</PaymentType>
                <SettleDate>2004-04-14T22:57:46.6230000-04:00</SettleDate>
                <CityName>Las Vegas</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12992</ID>
                <PaymentType>Cash</PaymentType>
                <SettleDate>2004-04-14T22:57:46.6230000-04:00</SettleDate>
                <CityName>New York</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12963</ID>
                <PaymentType>Check</PaymentType>
                <SettleDate>2004-04-14T22:57:51.3100000-04:00</SettleDate>
                <CityName>Orlando</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12962</ID>
                <PaymentType>Check</PaymentType>
                <SettleDate>2004-04-14T22:57:51.3100000-04:00</SettleDate>
                <CityName>New York</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12969</ID>
                <PaymentType>Credit Card</PaymentType>
                <SettleDate>2004-04-14T22:57:51.4830000-04:00</SettleDate>
                <CityName>Las Vegas</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12968</ID>
                <PaymentType>Voucher</PaymentType>
                <SettleDate>2004-04-14T22:57:51.4830000-04:00</SettleDate>
                <CityName>Orlando</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12975</ID>
                <PaymentType>Check</PaymentType>
                <SettleDate>2004-04-14T22:57:51.6400000-04:00</SettleDate>
                <CityName>Las Vegas</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12974</ID>
                <PaymentType>Check</PaymentType>
                <SettleDate>2004-04-14T22:57:51.6400000-04:00</SettleDate>
                <CityName>Orlando</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12981</ID>
                <PaymentType>Voucher</PaymentType>
                <SettleDate>2004-04-14T22:57:51.8100000-04:00</SettleDate>
                <CityName>New York</CityName>
        </AccountLineItem>
        <AccountLineItem>
                <ID>12980</ID>
                <PaymentType>Cash</PaymentType>
                <SettleDate>2004-04-14T22:57:51.8100000-04:00</SettleDate>
                <CityName>Orlando</CityName>
        </AccountLineItem>
</ArrayOfAccountLineItems>

II have been trying the for-each PaymentType[not(. =
preceding::PaymentType)] approach.

Any thoughts on the best way to tackle this?

Thanks.