I changed days to today, and they are added up correctly, however, I get 0% from the division.

The way your logic is set up, only one of $tracked_click or $tracked_impressions will be 1 when

  ($tracked_click*1) / ($tracked_impressions*1)
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is executed. The other will be zero. You're either going to divide zero by one, giving zero, or you're going to divide by zero. Is this really what you want to do?

Should I get rid of the </td /> and just use the regular code?

You should use </td>. The "trailing slash" form of tags is reserved for those tags that are not paired, like <br/>.