This is due to rounding.
AWS bills line item costs to the 6th decimal point (0.000001). CloudHealth reporting only considers costs to the 4th decimal point in cost (0.0001). This can lead to confusion regarding how these small charges show up on reports. Here is how CloudHealth reporting will treat each cost total:
0.005 to 0.009 will be presented as $0.01
0.0001 to 0.004 will be presented as $0.00 (clicking the hyperlink will show the breakdown of small charges in the Cost History drilldown)
0.000001 to 0.00009 will not show at all on reports