Do I need to open an account at my bank in order to do this? Or can I just withdraw physical cash?

I just looked at the NZD vs USD currency conversion and its about 4-5 cents USD difference from the buy and sell. I thought that was very high so looking to minimise that spread in the buy/sell.

Any help?

Just when experts say "bullish on the dollar" I'm wondering how us as NZ'ers can invest in the US dollar?

Thanks.