Depends on thee book, but most drop it to a 2 team teaser on a push.
Here is a read from another site on teasers:
Gamblers who think ten-point teasers are sucker bets consider that Las Vegas used to take full “three-team-ten-point teasers” in which ties won. Soon most switched to ties push or lose. Today we are hard pressed to find just one Vegas book that takes the old style three-team-ten-point teasers.
In most cases they do not even offer ten-points. In Vegas they are called super teasers and are really only available on teaser cards where the lines vary just seven to nine points from the spread. The sports books are here to make money and they knew they had a losing proposition. They cut out the winning advantages based on their percentages.
There are still a few places off-shore that take “three-team-ten-point teasers” in which ties push. These outs are gold. We never bet more than three teams in any teaser combination. In some weeks of the NFL season we only have wagers made as teasers with zero straight bets.
Teaser bets are particularly popular because the main attraction of a teaser bet is that it allows one to adjust the point spread in their favor. This entices or teases the bettor into making a play. Now we’ll be the first to admit that if a bettor blindly moves the line in making a teaser play without an understanding of line value they will be a longtime loser.
However if one has the knowledge of line value then the teaser bet can be a huge long term winner. We have found that NFL teasers in particular are an excellent way to maximize your profits.
We have been betting six, seven and ten point teasers for the past 15 years. Over that time a number of betting philosophies have changed in my approach. In the past we would nearly always bet the good teams teasing the points downward. We rarely took the points. However over the last three years that has changed as "parity" has entered the NFL landscape.
Favorites of ten points or more only covered only 65% of the time on a six or seven point teaser during the past three years. The NFL dogs have been barking a lot in the age of NFL parity.
Here are some obvious guidelines to help you win your share of teaser bets.
The most important thing with any teaser bet is to cross key numbers. It does not matter if you are playing a 6, 7 or 10 pointer. I can not begin to tell you how many times I have talked to a friend who incorrectly has bet a teaser and got plus-2.5 points or plus-6.5 points. In these situations it is obvious that there is not any value of key numbers like “three and seven are not gained. It does not matter if it is a six, seven or ten point teasers, one must cross or land on key numbers. In the NFL; three, seven and ten are the most important. If we can not put together a teaser that crosses key numbers we will skip the team and in some cases skip the bet.
In the NFL there are at least two weeks, if not more, where nearly all 32 potential sides cover a ten-point teaser spread. This means just about every teaser combination played wins. It is important to find "outs" that take these three-team-ten point teasers. It can only add money to your football bankroll.