When a relationship between two variables is proportional, it means that there is a constant ratio between the two variables. In this case, the answer is yes, there is a proportional relationship between total savings on gas and the number of beverages purchased.
You save $0.20 on gas for every beverage you buy.
Let s=dollars saved on gas, and b=# of beverages purchased
s=.2b
or
s=b/5