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 $68.26   6.201%   $72.4928   $72.49   $72.50   $72.50  
  Purchase #2 $211.99   9.781%   $232.7247   $232.72   $232.70   $232.70  
  Purchase #3 $83.97   11.482%   $93.6114   $93.61   $93.60   $93.60  
  Purchase #4 $21.65   4.587%   $22.6431   $22.64   $22.65   $22.60  
  Purchase #5 $157.81   13.177%   $178.6046   $178.60   $178.60   $178.60  
  Purchase #6 $222.38   10.217%   $245.1006   $245.10   $245.10   $245.10  
  Purchase #7 $65.25   11.655%   $72.8549   $72.85   $72.85   $72.90  
  7 purchase totals = $831.31       $918.0321   $918.01   $918.00   $918.00