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 $61.91   9.396%   $67.7271   $67.73   $67.75   $67.70  
  Purchase #2 $55.39   9.604%   $60.7097   $60.71   $60.70   $60.70  
  Purchase #3 $81.96   12.801%   $92.4517   $92.45   $92.45   $92.50  
  Purchase #4 $47.84   12.713%   $53.9219   $53.92   $53.90   $53.90  
  Purchase #5 $191.49   9.448%   $209.582   $209.58   $209.60   $209.60  
  Purchase #6 $190.32   11.588%   $212.3743   $212.37   $212.35   $212.40  
  Purchase #7 $108.62   4.385%   $113.383   $113.38   $113.40   $113.40  
  7 purchase totals = $737.53       $810.1497   $810.14   $810.15   $810.20