Use the modulo node.
LevelNumber % 10 == 0
The % is the modulo operator, your modulo node. Take the level number, send it through the modulo node and check if the result is 0. If it is the number has a 0 at the end.
To explain how it works:
Remember back in primary when you was taught to divide for the first time you did not care about decimals? You were counting remainders.
10/4=2 and 2 as remainder.
Similarly the modulo and divide node are linked to this.
10/4 = 2 10%4 = 2 10/3 = 3 10%3 = 1 510/10 = 51 510%10 = 0
Hope this makes it easier to understand.