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 $55.34   10.158%   $60.9614   $60.96   $60.95   $61.00  
  Purchase #2 $175.75   10.789%   $194.7117   $194.71   $194.70   $194.70  
  Purchase #3 $132.55   10.293%   $146.1934   $146.19   $146.20   $146.20  
  Purchase #4 $54.64   10.181%   $60.2029   $60.20   $60.20   $60.20  
  Purchase #5 $76.39   8.424%   $82.8251   $82.83   $82.85   $82.80  
  Purchase #6 $122.95   7.515%   $132.1897   $132.19   $132.20   $132.20  
  Purchase #7 $231.39   3.583%   $239.6807   $239.68   $239.70   $239.70  
  7 purchase totals = $849.01       $916.7649   $916.76   $916.80   $916.80