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 $32.63   6.469%   $34.7408   $34.74   $34.75   $34.70  
  Purchase #2 $236.69   5.408%   $249.4902   $249.49   $249.50   $249.50  
  Purchase #3 $212.51   6.105%   $225.4837   $225.48   $225.50   $225.50  
  Purchase #4 $196.91   11.185%   $218.9344   $218.93   $218.95   $218.90  
  Purchase #5 $8.61   4.162%   $8.9683   $8.97   $8.95   $9.00  
  Purchase #6 $125.98   13.517%   $143.0087   $143.01   $143.00   $143.00  
  Purchase #7 $67.62   12.828%   $76.2943   $76.29   $76.30   $76.30  
  7 purchase totals = $880.95       $956.9204   $956.91   $956.95   $956.90