Using this label format when I have zero values, appears a "-" character next to 0. I verified that is not a negative value, is 0. On iOS it looks nice.
<xForms:NumericalAxis.LabelStyle >
<xForms:ChartAxisLabelStyle TextColor="DarkGray" LabelFormat="0.0;-0.0"/>
</xForms:NumericalAxis.LabelStyle>
How it looks on Android: