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 $218.78   11.874%   $244.7579   $244.76   $244.75   $244.80  
  Purchase #2 $246.38   13.845%   $280.4913   $280.49   $280.50   $280.50  
  Purchase #3 $138.74   11.493%   $154.6854   $154.69   $154.70   $154.70  
  Purchase #4 $214.40   9.229%   $234.187   $234.19   $234.20   $234.20  
  Purchase #5 $241.95   13.420%   $274.4197   $274.42   $274.40   $274.40  
  Purchase #6 $13.96   5.113%   $14.6738   $14.67   $14.65   $14.70  
  Purchase #7 $245.80   6.263%   $261.1945   $261.19   $261.20   $261.20  
  7 purchase totals = $1,320.01       $1,464.4096   $1,464.41   $1,464.40   $1,464.50