Yes, clear tape is fine but there is a BETTER option.
On the USPS website you can order supplies free.
You can order by the pack of 50 clear plastic sleeves (customs form) but the postal services is OK with these being used on all packages.
Simply place your label inside, peel off the back, stick on box.
Best part, again, these are FREE and the P.O. will deliver them to you free as well.