Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $110.46   13.321%   $125.1744   $125.17   $125.15   $125.20  
  Purchase #2 $160.38   10.133%   $176.6313   $176.63   $176.65   $176.60  
  Purchase #3 $73.36   8.671%   $79.721   $79.72   $79.70   $79.70  
  Purchase #4 $89.50   13.625%   $101.6944   $101.69   $101.70   $101.70  
  Purchase #5 $110.29   5.757%   $116.6394   $116.64   $116.65   $116.60  
  Purchase #6 $58.74   6.510%   $62.564   $62.56   $62.55   $62.60  
  Purchase #7 $207.71   13.476%   $235.701   $235.70   $235.70   $235.70  
  7 purchase totals = $810.44       $898.1255   $898.11   $898.10   $898.10