Unless your parents are super strict I doubt they will get mad about those $5. All you need to tell them is you bought a one month premium membership to an anime site. Your membership doesn't require you to have it but if you want to buy a month it is $5. Don't tell them you HAVE to get premium otherwise they will be like "Hell No." Tell them you only got it to get a bigger avatar. Tell them you are sorry and they should be like "No problem. Thank you for being honest."
Ofc if you are from a hispanic family like my friend, your parents will freak out and tell you they barely have money to pay the bills and you are out wasting it like nothing and on a stupid computer. Then you will get grounded and you can never come to NB again.
XD
Note: Not being racist but it is funny what my friends family gets mad about. ^^