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 $247.43   5.753%   $261.6646   $261.66   $261.65   $261.70  
  Purchase #2 $120.81   4.371%   $126.0906   $126.09   $126.10   $126.10  
  Purchase #3 $190.55   10.294%   $210.1652   $210.17   $210.15   $210.20  
  Purchase #4 $137.81   6.625%   $146.9399   $146.94   $146.95   $146.90  
  Purchase #5 $43.73   10.189%   $48.1856   $48.19   $48.20   $48.20  
  Purchase #6 $195.27   6.427%   $207.82   $207.82   $207.80   $207.80  
  Purchase #7 $197.93   8.372%   $214.5007   $214.50   $214.50   $214.50  
  7 purchase totals = $1,133.53       $1,215.3666   $1,215.37   $1,215.35   $1,215.40