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 $32.56   6.242%   $34.5924   $34.59   $34.60   $34.60  
  Purchase #2 $247.97   5.530%   $261.6827   $261.68   $261.70   $261.70  
  Purchase #3 $52.60   7.727%   $56.6644   $56.66   $56.65   $56.70  
  Purchase #4 $167.74   3.272%   $173.2285   $173.23   $173.25   $173.20  
  Purchase #5 $30.64   9.428%   $33.5287   $33.53   $33.55   $33.50  
  Purchase #6 $39.99   11.296%   $44.5073   $44.51   $44.50   $44.50  
  Purchase #7 $61.92   13.465%   $70.2575   $70.26   $70.25   $70.30  
  7 purchase totals = $633.42       $674.4615   $674.46   $674.50   $674.50