There are already quite a few Instructables showing how to make origami ninja stars but none that I could find using dollar bills. Though making these with dollar bills is pretty much the same as with paper, there are a few differences so I decided to show how I make them.
Hopefully the pictures and captions explain how to fold these but I've provided written explanation as well. If you can fold them just using the pictures then don't read the text (it's boring) but know that it's there incase you get stuck.
Usually when I make a ninja star I start from the ends of the bill and work in. When I tried to make one out of dollar bills I realized that they have to folded from the center instead because of the different dimension of the bill versus a 1:2 sided rectangle. To get the 1:2 ratio, part of the bill has to be doubled up. I thought of folding this part from the start but I later figured out a better time to do it that provided a fold guide.
Step 1: Materials
Fold the bill in half hot dog style.
Fold the bill in half hamburger style then unfold.
Step 3: Bill #1
Bring down the upper right side to meet the middle crease.
Flip the bill over.
Step 4: Bill #1 Continued
Fold the flap where the border of the bill design is back.
Unfold the first crease made in this step and keep that flap near the border folded down.
Re-crease the first fold and you'll have a triangle point.
Repeat these steps on the other end, diagonally folding, creasing the flap, opening, and re-creasing to create a clean triangle point.
You're now done with bill #1. When you flip the bill over you will see two large triangles.
Step 5: Bill #2
Fold the two edges into the middle and flip the bill over.
Fold the ends on the diagonal, left side down, right side up.
Fold the excess flaps behind and tuck in.
If done correctly, when the bill is flipped over you will again see two triangles.
Step 6: Putting It All Together
Lay down a bill in the position shown in the first picture. Put the second bill, two triangles side facing up, on top of the other bill.
Bring down the small top triangle of the bottom bill and tuck it under the big triangle of the bill on top (picture 3). Fold up the bottom small triangle and tuck into the other big triangle (picture 4). Flip the model over.
Bring the triangle flap on the left side down and tuck into the middle crease. Tuck the right triangle flap into the middle crease too. Adjust the bills a little if you need to and have fun throwing your money around.