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 $218.34   12.775%   $246.2329   $246.23   $246.25   $246.20  
  Purchase #2 $248.61   10.844%   $275.5693   $275.57   $275.55   $275.60  
  Purchase #3 $24.90   12.109%   $27.9151   $27.92   $27.90   $27.90  
  Purchase #4 $247.82   5.384%   $261.1626   $261.16   $261.15   $261.20  
  Purchase #5 $222.42   12.339%   $249.8644   $249.86   $249.85   $249.90  
  Purchase #6 $215.72   10.250%   $237.8313   $237.83   $237.85   $237.80  
  Purchase #7 $216.85   6.720%   $231.4223   $231.42   $231.40   $231.40  
  7 purchase totals = $1,394.66       $1,529.9979   $1,529.99   $1,529.95   $1,530.00