You received a number of shares that had some value per share. It therefore had a total $ value (# shares x NAV). The total value is what is important, here. *That* is added to the cost basis since you will be paying taxes on this.
The point that John was making is that the cost per share that was reported is almost certainly rounded off from the actual cost. Most of the time they round off to, for example, 3 or 4 decimal places. In actuality, though, they track it in 5,6 or more decimal paces. This means that if you multiply the number of shares by the cost per share as reported, you will be over or under calculating the total value.
If you have the total value of the reinvestment, then enter the number of shares and the total value and let Q calculate the NAV. If all you have is the number and NAV, then enter them and accept the total value. If you can figure it out later, re-enter the data to get the *right* value.
Really, though, if you look at the overall picture, I doubt that either way will make much of a difference. The difference in cost basis is going to be so small that the tax consequences (and *that* is what is important) will be small or non-existent....