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 $227.82   6.202%   $241.9494   $241.95   $241.95   $241.90  
  Purchase #2 $97.38   3.452%   $100.7416   $100.74   $100.75   $100.70  
  Purchase #3 $18.98   6.617%   $20.2359   $20.24   $20.25   $20.20  
  Purchase #4 $182.85   5.590%   $193.0713   $193.07   $193.05   $193.10  
  Purchase #5 $115.39   3.597%   $119.5406   $119.54   $119.55   $119.50  
  Purchase #6 $57.69   13.411%   $65.4268   $65.43   $65.45   $65.40  
  Purchase #7 $198.57   8.630%   $215.7066   $215.71   $215.70   $215.70  
  7 purchase totals = $898.68       $956.6722   $956.68   $956.70   $956.50