Either tap on or press 'A' next to the town fountain to deposit coins. After a certain total is achieved something is unlocked.

Unlockable	How to unlock
10 Extra Lives	6000
2 Extra Lives	200
20 Extra Lives	8000
5 Extra Lives	500
Developer's Grove (town)	10000
Music available "Alt."	7000
Music available "City Funk"	3000
Music available "Special"	1000
Palette available "Horizontal"	2000
Stamp available "Shape2"	5000