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 $61.41   6.105%   $65.1591   $65.16   $65.15   $65.20  
  Purchase #2 $242.63   7.354%   $260.473   $260.47   $260.45   $260.50  
  Purchase #3 $50.80   13.577%   $57.6971   $57.70   $57.70   $57.70  
  Purchase #4 $21.62   4.528%   $22.599   $22.60   $22.60   $22.60  
  Purchase #5 $168.46   12.790%   $190.006   $190.01   $190.00   $190.00  
  Purchase #6 $20.46   11.280%   $22.7679   $22.77   $22.75   $22.80  
  Purchase #7 $247.32   13.857%   $281.5911   $281.59   $281.60   $281.60  
  7 purchase totals = $812.70       $900.2932   $900.30   $900.25   $900.40