The Pressero system uses the "Banker's rounding" approach for rounding dollar amounts. This is also known as the half-to-even rounding approach. As an example, if the total taxes on an order came to $9.235, Pressero would round this to $9.24. However, if the total taxes were $9.245 would also be rounded to $9.24. Please see this article for further explanation: http://en.wikipedia.org/wiki/Rounding#Round_half_to_even)
This is generally considered the best rounding system for money.