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 $245.69   6.105%   $260.6894   $260.69   $260.70   $260.70  
  Purchase #2 $5.88   10.459%   $6.495   $6.50   $6.50   $6.50  
  Purchase #3 $136.42   5.507%   $143.9326   $143.93   $143.95   $143.90  
  Purchase #4 $5.63   11.687%   $6.288   $6.29   $6.30   $6.30  
  Purchase #5 $182.25   8.601%   $197.9253   $197.93   $197.95   $197.90  
  Purchase #6 $97.56   7.128%   $104.5141   $104.51   $104.50   $104.50  
  Purchase #7 $37.60   12.277%   $42.2162   $42.22   $42.20   $42.20  
  7 purchase totals = $711.03       $762.0606   $762.07   $762.10   $762.00