I'm looking into NoSQL for scaling alternatives to a database. What do I do if I want transaction-based things that are sensitive to these kind of things?
Generally speaking, NoSQL solutions have lighter weight transactional semantics than relational databases, but still have facilities for atomic operations at some level.
Generally, the ones which do master-master replication provide less in the way of consistency, and more availability. So one should choose the right tool for the right problem.
Many offer transactions at the single document (or row etc.) level. For example with MongoDB there is atomicity at the single document - but documents can be fairly rich so this usually works pretty well -- more info here.