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 $239.98   9.115%   $261.8542   $261.85   $261.85   $261.90  
  Purchase #2 $130.39   7.421%   $140.0662   $140.07   $140.05   $140.10  
  Purchase #3 $204.26   9.796%   $224.2693   $224.27   $224.25   $224.30  
  Purchase #4 $51.77   5.105%   $54.4129   $54.41   $54.40   $54.40  
  Purchase #5 $189.71   9.110%   $206.9926   $206.99   $207.00   $207.00  
  Purchase #6 $246.56   11.396%   $274.658   $274.66   $274.65   $274.70  
  Purchase #7 $88.57   12.546%   $99.682   $99.68   $99.70   $99.70  
  7 purchase totals = $1,151.24       $1,261.9352   $1,261.93   $1,261.90   $1,262.10