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 $59.63   8.571%   $64.7409   $64.74   $64.75   $64.70  
  Purchase #2 $231.96   10.684%   $256.7426   $256.74   $256.75   $256.70  
  Purchase #3 $164.41   11.203%   $182.8289   $182.83   $182.85   $182.80  
  Purchase #4 $60.80   3.314%   $62.8149   $62.81   $62.80   $62.80  
  Purchase #5 $65.88   7.162%   $70.5983   $70.60   $70.60   $70.60  
  Purchase #6 $25.27   9.112%   $27.5726   $27.57   $27.55   $27.60  
  Purchase #7 $74.84   7.508%   $80.459   $80.46   $80.45   $80.50  
  7 purchase totals = $682.79       $745.7572   $745.75   $745.75   $745.70