why did you get new tires?
if the old ones were showing abnormal wear, then an alignment would be OK. BUT, you don't definitely, for sure, must have, 'cause the salesman says so. an alignment.
on the other hand, how much did you spend on new rubber? might just well be worth having an alignment done to eliminate tire wear as a potential problem.
you should ALWAYS regularly rotate your tires, to minimize abnormal wear, and this helps remove the tire wear from the equation.