Being generous to a certain extent is an investment. The old adage "the more you give, the more you receive" holds some truth. There are ways of explaining it. It could be explained from a spiritual point of view. It could also be explained in terms of character-building and ways to attract people and spread positive vibration. And it could also be explained from a business point of view.
I guess the last one is the thing that matters in this discussion. I've had numerous encounters that somehow prove that "the more you give, the more you receive." For one, the more you provide discounts to your goods or services, the more customers would buy from you. Another thing, in the government agency that I used to work, the more generous the supplier or contractor is, the more contracts they will get. In sales, for example, the more you treat your clients, the more you bring gifts to them, the more they will stick to your brand. As a matter of fact, I have a friend who worked as a medical representative and he said that whatever doctors request, may it be a planner, a laptop or desktop, an expensive meal in a newly-opened restaurant, and others, give it to them. That's one way of selling your product. I have a lot to share but, lastly, I used to work in a non-government organization and we had a lot of generous donors, many of them businessmen. Every time we need to buy something in huge amounts, we wouldn't go elsewhere but to our donors.
So this is probably the explanation. However, I have reservations when you simply say:
The moment I started donating regularly and making extraordinary donations, also giving unexpected tips, etc., my personal finances, which were already going well, got a boost.