Answer:
The pattern is that multiples of 5 either have a 5 or a 0 in the ones place
Explanation:
One $5 -> total is $5 (a five in the ones place)
Two $5s -> total is $10 (a 0 in the ones place)
Three $5s -> total is $15 (a five in the ones place)
Four $5s -> total is $20 (a 0 in the ones place)
Five $5 -> total is $25 (a five in the ones place)
Six $5s -> total is $30 (a 0 in the ones place)