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 $241.69   10.782%   $267.749   $267.75   $267.75   $267.70  
  Purchase #2 $246.81   13.541%   $280.2305   $280.23   $280.25   $280.20  
  Purchase #3 $229.30   11.278%   $255.1605   $255.16   $255.15   $255.20  
  Purchase #4 $27.46   11.709%   $30.6753   $30.68   $30.70   $30.70  
  Purchase #5 $58.53   3.395%   $60.5171   $60.52   $60.50   $60.50  
  Purchase #6 $237.73   3.792%   $246.7447   $246.74   $246.75   $246.70  
  Purchase #7 $250.85   3.319%   $259.1757   $259.18   $259.20   $259.20  
  7 purchase totals = $1,292.37       $1,400.2528   $1,400.26   $1,400.30   $1,400.20