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 $60.39   11.430%   $67.2926   $67.29   $67.30   $67.30  
  Purchase #2 $92.82   10.494%   $102.5605   $102.56   $102.55   $102.60  
  Purchase #3 $14.69   13.448%   $16.6655   $16.67   $16.65   $16.70  
  Purchase #4 $106.73   5.517%   $112.6183   $112.62   $112.60   $112.60  
  Purchase #5 $141.41   13.804%   $160.9302   $160.93   $160.95   $160.90  
  Purchase #6 $222.81   12.188%   $249.9661   $249.97   $249.95   $250.00  
  Purchase #7 $163.84   11.856%   $183.2649   $183.26   $183.25   $183.30  
  7 purchase totals = $802.69       $893.2981   $893.30   $893.25   $893.40