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 $67.27   13.189%   $76.1422   $76.14   $76.15   $76.10  
  Purchase #2 $247.31   5.644%   $261.2682   $261.27   $261.25   $261.30  
  Purchase #3 $106.45   10.167%   $117.2728   $117.27   $117.25   $117.30  
  Purchase #4 $122.94   13.674%   $139.7508   $139.75   $139.75   $139.80  
  Purchase #5 $85.82   10.343%   $94.6964   $94.70   $94.70   $94.70  
  Purchase #6 $74.82   13.273%   $84.7509   $84.75   $84.75   $84.80  
  Purchase #7 $109.40   13.280%   $123.9283   $123.93   $123.95   $123.90  
  7 purchase totals = $814.01       $897.8096   $897.81   $897.80   $897.90