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 $55.97   11.669%   $62.5011   $62.50   $62.50   $62.50  
  Purchase #2 $211.44   13.143%   $239.2296   $239.23   $239.25   $239.20  
  Purchase #3 $60.56   10.574%   $66.9636   $66.96   $66.95   $67.00  
  Purchase #4 $18.42   8.679%   $20.0187   $20.02   $20.00   $20.00  
  Purchase #5 $25.39   8.755%   $27.6129   $27.61   $27.60   $27.60  
  Purchase #6 $58.92   8.138%   $63.7149   $63.71   $63.70   $63.70  
  Purchase #7 $231.86   9.327%   $253.4856   $253.49   $253.50   $253.50  
  7 purchase totals = $662.56       $733.5264   $733.52   $733.50   $733.50