You have 3 answers already, but I'll add another one! I'm sure you know what pennies are, they are small coins that are worth the least amount of money. It is a tradition in many countries to throw money into water and make a wish. The idea is that you are throwing away something of value and hoping that it will pay for some good luck. This is just a superstitious tradition. If people really believed you could buy good luck they would throw thousands of dollars and not just pennies. You can describe pennies in other ways... "Pocketed pennies" <--pennies you have put in your pocket "Invested pennies" <--pennies you have invested in a business "Wasted pennies" <--pennies you lost or spent or gave away without getting anything back. So "thrown pennies" refers to pennies you have thrown into water, hoping it will bring you some luck.

The other answers are correct, but here is a cultural act, where someone throws pennies, or coins into a well, or fountain. In return the thrower makes a wish. Depending on the context, it could refer to this as well.

为了一分钱的表演

This means someone is performing, maybe a musician on the street, and people throw coins to the performer.

A 'penny' is (was) a very small coin worth almost nothing. You could buy little to nothing with it. 'for thrown small pennies' is an expression derived from this. It means to 'throw' or invest only a little money at something. It essentially means if you only assign/invest/give a tiny amount of money at something, then you should expect only very little in return. It can be used literally (you only physically spend a tiny amount of money and get little in return) or sometimes metaphoricaly (Rather than little money, you are investing little effort or time and the result is negligible as well) Examples: (1) I only spent a small amount of money on renovating my house. I can expect little (in return) for the pennies thrown'. I am saying I spent very little, therefore I should expect little in return. (2) "I hardly studied for the exam so for the pennies thrown, my failure was expected." I put little to no effort into studying, so my failure was only to be expected.