If you just got them home from the pet store they are likely very stressed and not at the top of their health either. Pet stores tend to be less clean than home cages, more over crowded and a lot more fighting for food and water. As well, overcroweded rats tend to spread germs more of course.

Make sure they are not on cedar bedding (many bedding mixes contain a lot of cedar though don't always say they are cedar). Pine is okay, aspen is best. Just make sure you don't have them overcrowded or in a very small enclosure. Make sure their enclosure is well vented for the amonia in their urine but not drafty (if a cat would be comfie at the room temp so would a rat basically). Give them tons of fresh water and good food and let them settle in. Watch for indications that the sneezing isn't going away, they have an excess of red tears or nasal discharge (it's not blood), or they have very loose stools. Also if they appear hunched up or their guard hairs are up constantly so they look out of sorts or their hair is very patchy. Those are things to worry about really. If the sneezing is just stress and poor husbandry related it should pass fairly quickly given good care by you.