“I am in Zimbabwe for one week now and I have used just US$. Try to pay everything you can by credit card and souvenirs, taxis, tips in US$. Bring small US$ denominations and be prepared to negotiate the taxi cost and the craft souvenir prices.”  – TripAdvisor User

1 USD = 361 ZDW (Zimbabwean Dollar)
1 USD = 27.94 Kwacha (Zambia Dollars)

Both Tanzanian shillings and US dollars are accepted as cash for payment almost everywhere.
“For the most part you need to use either US Dollars or the local currency T Shillings. I always advise using T Shilling while you are there, you will get the best rates from this. Can you use dollars, sure, but some will discount them heavily; for example if something was 1,000 T Shillings, they might accept $1 for it (when the exchange rate is actually 1,375 TSh = $1) so that’s over a 30% discount for using dollars.”  – TripAdvisor User

1 USD = 2,545.83 TZS (Tanzania Shilling)

All hard currencies are welcome but dollars are perhaps more welcome than others. In any case, if you’re coming from the US, dollars are the obvious choice. The airport bank where you buy visas will change money at reasonable rates, maybe not quite as reasonable as downtown banks but reasonable nonetheless.

1 USD = 50.22 EGP (Egyptian Pound)