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 $56.91   11.677%   $63.5554   $63.56   $63.55   $63.60  
  Purchase #2 $224.73   10.292%   $247.8592   $247.86   $247.85   $247.90  
  Purchase #3 $241.96   3.300%   $249.9447   $249.94   $249.95   $249.90  
  Purchase #4 $149.96   12.528%   $168.747   $168.75   $168.75   $168.70  
  Purchase #5 $109.86   9.171%   $119.9353   $119.94   $119.95   $119.90  
  Purchase #6 $169.56   11.699%   $189.3968   $189.40   $189.40   $189.40  
  Purchase #7 $83.90   10.472%   $92.686   $92.69   $92.70   $92.70  
  7 purchase totals = $1,036.88       $1,132.1244   $1,132.14   $1,132.15   $1,132.10