I work in a microbiology lab where we do a lot of cloning. I have always used restriction endonucleases to cleave the DNA to have sticky ends and not blunt ends. I currently am working on a project that suggests using a blunt end restriction enzyme, such as EvoRV, and then to perform a T-tailing of the plasmid, pl4440. My question is why do I not treat my pcr'd insert with a restriction digest just like I would the plasmid as the protocol suggests? How do I know the insert has ends that are able to ligate into the plasmid if I don't design the restriction sites into the primers?
To know if the ends are compatible see compatible cohesive ends (isoschizomers) from NEB website.
If you are unsure then do a blunt end ligation. For blunting a sticky end (From the comments):
Use Klenow or Pfu polymerase (or any proofreading/high fidelity polymerase).
You can use Taq if you intend to to a TA cloning.