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 $67.99   12.463%   $76.4636   $76.46   $76.45   $76.50  
  Purchase #2 $164.80   4.102%   $171.5601   $171.56   $171.55   $171.60  
  Purchase #3 $160.59   12.419%   $180.5337   $180.53   $180.55   $180.50  
  Purchase #4 $83.38   13.593%   $94.7138   $94.71   $94.70   $94.70  
  Purchase #5 $146.96   12.250%   $164.9626   $164.96   $164.95   $165.00  
  Purchase #6 $6.76   13.583%   $7.6782   $7.68   $7.70   $7.70  
  Purchase #7 $69.86   5.432%   $73.6548   $73.65   $73.65   $73.70  
  7 purchase totals = $700.34       $769.5668   $769.55   $769.55   $769.70