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 $62.63   12.755%   $70.6185   $70.62   $70.60   $70.60  
  Purchase #2 $60.95   13.534%   $69.199   $69.20   $69.20   $69.20  
  Purchase #3 $53.70   11.620%   $59.9399   $59.94   $59.95   $59.90  
  Purchase #4 $69.82   10.251%   $76.9772   $76.98   $77.00   $77.00  
  Purchase #5 $163.81   9.780%   $179.8306   $179.83   $179.85   $179.80  
  Purchase #6 $210.45   3.304%   $217.4033   $217.40   $217.40   $217.40  
  Purchase #7 $65.51   7.571%   $70.4698   $70.47   $70.45   $70.50  
  7 purchase totals = $686.87       $744.4383   $744.44   $744.45   $744.40