I want to buy a car with part of our taxes
Why is that how you want to spend your taxes?
I mean that my partner and I should rejoice in our shared resources
It's best you speak about and get confirmation on your purchase from your partner first before using the money. It could cause a lot of problems if you do with without consulting them.
I'm doing this because I care about the community
It's good that you want to help the local economy and have some fun with your money, but the point remains that this money is a shared resource.  You should consult your partner about how to use the money, as you may have pressing obligations that you need to save it for.