If you're so inclined, you can also use Marriott Rewards points to purchase Marriott Gift Cards, which never expire worthless (as the Cheques can) and which do allow you to "pay" exact charges without losing "change" (the Gift Cards are stored-value VISA cards, so you can use them to pay the same way you'd use a VISA card, and use them over and over until the value is all used up).
Prices are a bit steep, though, in my opinion:
$50 card is 20,000 points;
$100 card is 35,000 points;
$200 card is 59,000 points;
$500 card is 100,000 points; and
$1000 card is 190,000 points.
This link may take you there (or it may only work for someone who is signed in).