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 $64.69   13.145%   $73.1935   $73.19   $73.20   $73.20  
  Purchase #2 $221.83   11.524%   $247.3937   $247.39   $247.40   $247.40  
  Purchase #3 $186.91   4.270%   $194.8911   $194.89   $194.90   $194.90  
  Purchase #4 $126.25   13.490%   $143.2811   $143.28   $143.30   $143.30  
  Purchase #5 $56.83   4.152%   $59.1896   $59.19   $59.20   $59.20  
  Purchase #6 $154.54   13.816%   $175.8912   $175.89   $175.90   $175.90  
  Purchase #7 $94.93   7.240%   $101.8029   $101.80   $101.80   $101.80  
  7 purchase totals = $905.98       $995.6431   $995.63   $995.70   $995.70