When you order 10 quantity of xxx for 0.002, and when there is only 2 items up for sale, the exchange processes those two and puts 8 in the buy queue at the buy price of 0.002. It does not take into consideration the quantity of the .0015 and .001 items for sale. You are not buying for .002 or less... you are buying for .002

I believe all exchange does their transaction like this. Correct me if I'm wrong. I haven't seen an exchange where you can have an option for equal to / less than a desired price.