Well personally it would take me a couple of seconds to get to "roughly 85c/month", but I wouldn't actually be thinking that when deciding to signup.
However, if I did care about how much $9.99/year is each month, rather than even trying to be slightly accurate, I'd round it off as "less than a dollar a month" and go straight ahead. That extra 17c/month doesn't make a difference to me.
(Obviously both my calculations speed and the amount I care about price differences when talking about that amount of money isn't neccesarily equal to that of other, possibly most other, potential customers.)
However, if I did care about how much $9.99/year is each month, rather than even trying to be slightly accurate, I'd round it off as "less than a dollar a month" and go straight ahead. That extra 17c/month doesn't make a difference to me.
(Obviously both my calculations speed and the amount I care about price differences when talking about that amount of money isn't neccesarily equal to that of other, possibly most other, potential customers.)