Just a little change:
1 digit: 15% prize (chances 1/10)
2 digits: 15% prize (chances 1/100)
3 digits: 15% prize (chances 1/1000)
4 digits: 15% prize (chances 1/10000)
all 5 digits: 15% prize (chances 1/100000)
results:
many people happy with just 1 or 2 right digits
still an huge amount of money for who guess all 5 digits