I figured it out. I wanted to round it off too. No decimal places.
You have to edit the template files. look for the showPrecipitationAmount if statement. I altered the output a little bit… see below for what I did.
in forecast.njk
{% if config.showPrecipitationAmount %}
{% if f.precipitationUnits %}
<td class="align-right bright precipitation">
{{ f.precipitation }}{{ f.precipitationUnits }}
</td>
{% else %}
{% if f.pop %}
<td class="align-right precipitation">
{{(f.pop * 100).toFixed(0)}}%
</td>
{% endif %}
<td class="align-right bright precipitation">
{{ f.precipitation | unit("precip") }}
</td>
{% endif %}
{% endif %}
I found info on the templates by googling nunchucks templates.