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 $21.65   6.104%   $22.9715   $22.97   $22.95   $23.00  
  Purchase #2 $67.85   12.859%   $76.5748   $76.57   $76.55   $76.60  
  Purchase #3 $121.56   12.419%   $136.6565   $136.66   $136.65   $136.70  
  Purchase #4 $118.25   3.800%   $122.7435   $122.74   $122.75   $122.70  
  Purchase #5 $13.38   7.396%   $14.3696   $14.37   $14.35   $14.40  
  Purchase #6 $139.83   4.143%   $145.6232   $145.62   $145.60   $145.60  
  Purchase #7 $40.46   12.255%   $45.4184   $45.42   $45.40   $45.40  
  7 purchase totals = $522.98       $564.3575   $564.35   $564.25   $564.40