100  clicks will only give you a rough idea of conversion. To a 90% confidence (meaning the real answer is outside the range 1 in 10 times) here is what you get

none of which are particularly narrow ranges, I would suggest assuming the low end to start.)
                 Sales    Test CR   Confidence 
  
     error   -   +                   1    1.00%   90%   
  1.970%   -0.97%   2.97%                   2    2.00%   90%   
  2.37%   -0.37%   4.37%                   3    3.00%   90%   
  2.69%   0.31%   5.69%                   4    4.00%   90%   
  2.95%   1.05%   6.95%                   5    5.00%   90%   
  3.18%   1.82%   8.18%                   6    6.00%   90%   
  3.38%   2.62%   9.38%                   7    7.00%   90%   
  3.57%   3.43%   10.57%                   8    8.00%   90%   
  3.74%   4.26%   11.74%                   9    9.00%   90%   
  3.89%   5.11%   12.89%                 10    10.00%   90%   
  4.03%   5.97%   14.03%
Bah the table looks like shit...suffice it to say that 100 clicks will give you only a rough idea, the higher the conversion rate, the wider the margin of error.