Toyota requires you use 0w-20 synthetic (I don't think there is a "regular" 0w-20 anyways) in your vehicle. Using any oil other than the recommended oil in the service manual (there are charts for certain temperature/climate zones to use a different oil) will void your warranty should an engine failure occur and they WILL test your oil.
That being said, the engine WAS designed and built to use 0w-20 oil and it will operate best using that weight of oil. Just be thankful Toyota only cares about the weight unlike say VW, Mercedes, GM, BMW, ect ect that now require you to use their super special secret version $$$$$$ oil to have the vehicle function properly and maintain warranty.