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 $217.93   13.149%   $246.5856   $246.59   $246.60   $246.60  
  Purchase #2 $235.91   13.149%   $266.9298   $266.93   $266.95   $266.90  
  Purchase #3 $209.38   10.401%   $231.1576   $231.16   $231.15   $231.20  
  Purchase #4 $222.32   9.628%   $243.725   $243.73   $243.75   $243.70  
  Purchase #5 $25.69   5.105%   $27.0015   $27.00   $27.00   $27.00  
  Purchase #6 $151.87   8.619%   $164.9597   $164.96   $164.95   $165.00  
  Purchase #7 $49.91   10.564%   $55.1825   $55.18   $55.20   $55.20  
  7 purchase totals = $1,113.01       $1,235.5417   $1,235.55   $1,235.60   $1,235.60