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 $231.96   6.750%   $247.6173   $247.62   $247.60   $247.60  
  Purchase #2 $197.69   11.208%   $219.8471   $219.85   $219.85   $219.80  
  Purchase #3 $74.63   13.539%   $84.7342   $84.73   $84.75   $84.70  
  Purchase #4 $44.94   5.229%   $47.2899   $47.29   $47.30   $47.30  
  Purchase #5 $234.86   9.258%   $256.6033   $256.60   $256.60   $256.60  
  Purchase #6 $250.58   4.448%   $261.7258   $261.73   $261.75   $261.70  
  Purchase #7 $219.28   13.632%   $249.1722   $249.17   $249.15   $249.20  
  7 purchase totals = $1,253.94       $1,366.9898   $1,366.99   $1,367.00   $1,366.90