This depends on what the problem is. If it is like example #1, where both numbers have zeroes on the ends, then you do not need to include the zero. However, if the problem is like example #2, and one number has a zero, and one does not, then you would have to include a zero on both. Just make sure that you line up your numbers correctly!
2.50
3.30
+____
5.80
= 5.8
2.8 ←(you would include a zero here)
3.10
+____
5.90
= 5.9
