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 $67.73   6.248%   $71.9618   $71.96   $71.95   $72.00  
  Purchase #2 $146.60   6.713%   $156.4413   $156.44   $156.45   $156.40  
  Purchase #3 $46.27   6.316%   $49.1924   $49.19   $49.20   $49.20  
  Purchase #4 $26.62   3.488%   $27.5485   $27.55   $27.55   $27.50  
  Purchase #5 $165.63   3.287%   $171.0743   $171.07   $171.05   $171.10  
  Purchase #6 $169.71   10.107%   $186.8626   $186.86   $186.85   $186.90  
  Purchase #7 $121.95   7.578%   $131.1914   $131.19   $131.20   $131.20  
  7 purchase totals = $744.51       $794.2723   $794.26   $794.25   $794.30