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 $73.42   4.552%   $76.7621   $76.76   $76.75   $76.80  
  Purchase #2 $234.96   11.395%   $261.7337   $261.73   $261.75   $261.70  
  Purchase #3 $61.34   13.540%   $69.6454   $69.65   $69.65   $69.60  
  Purchase #4 $24.71   8.149%   $26.7236   $26.72   $26.70   $26.70  
  Purchase #5 $92.85   9.655%   $101.8147   $101.81   $101.80   $101.80  
  Purchase #6 $112.61   7.465%   $121.0163   $121.02   $121.00   $121.00  
  Purchase #7 $82.63   12.482%   $92.9439   $92.94   $92.95   $92.90  
  7 purchase totals = $682.52       $750.6397   $750.63   $750.60   $750.50