I was sceptical about psychological pricing until I worked at a call centre and had this conversation multiple times a week.

Caller: Why is my bill £10 higher this month?
Me: I see you made a £2 call to a premium rate number
Caller: That's only £2.
Me: Yes, your bill is normally £19.99 a month. Add on the £2 and you get £21.99, which is what you paid this month.
Caller: (notices the other digits) Oh, so it is.