Initialise two counters, fives and tens to keep track of the number of 5$ and 10$ bills at hand. Initialise them to zero as we hold no change at the starting.
Loop through each bill in the bills array and check the following: If the bill is 5$, increment the fives counter.
If the bill is 10$, check if there are any 5$ bills available.

If yes, provide change by incrementing the 10$ bill counter and decrementing the 5$ bill counter.
If there are no 5$ bills available, return false as we cannot provide change.

If the current bill is 20$, check if both 5$ and 10$ bills are available. If yes, provide change by decreasing the counter of 5$ and 10$ bills.

If there are not enough 10$ bills available, check if there are at atleast three 5$ bills available. If yes, provide change by decreasing the 5$ counter by 3.
If not able to provide change, return false.

If all customers are served with the correct change, we exit out of the loop and return true.