Although recent studies have shown that since we finally improved paper currency's sturdiness the $1 bill is lasting long enough now to be worth keeping around.[1]
We really should be using $1, $2, $5 and $10 coins
No penny; typical nickles, dimes, and quarters; loonies and toonies ($1 and $2 coins); as well as very durable and fancily-secured polymer bills for $5, $10, $20, $50, and $100.
The only complaint might be that all the bills are the same size instead of on a log-scale like eu or aus, but I prefer it that way.
I wouldn't see much value in coins >$2, bills are far simpler to carry and don't make noise or scratch screens.
2 NZD ~= 1.40 USD.
Note that NZ’s smallest coin is 10 cents - it is good not having pennys nor nickels.