The earnings you see are rounded up or rounded down figures.

The sum is CPM divided by 1000, then multiplied by the number of views.

So your earnings may in actual fact be .066+.076 +.126 which would show as .07, .08, .13 (=.28) instead of the real sum of .268 which would read as .27 when rounded up.

HP work their payments out in monthly totals (even though they show daily), so unless you use a spreadsheet that allows for more than 2 decimal points, you will not see the correct sum.