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 $191.76   7.683%   $206.4929   $206.49   $206.50   $206.50  
  Purchase #2 $108.39   7.326%   $116.3307   $116.33   $116.35   $116.30  
  Purchase #3 $96.74   12.712%   $109.0376   $109.04   $109.05   $109.00  
  Purchase #4 $103.78   10.684%   $114.8679   $114.87   $114.85   $114.90  
  Purchase #5 $63.46   4.565%   $66.3569   $66.36   $66.35   $66.40  
  Purchase #6 $218.67   10.193%   $240.959   $240.96   $240.95   $241.00  
  Purchase #7 $72.28   12.347%   $81.2044   $81.20   $81.20   $81.20  
  7 purchase totals = $855.08       $935.2494   $935.25   $935.25   $935.30