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 $242.97   10.779%   $269.1597   $269.16   $269.15   $269.20  
  Purchase #2 $56.67   10.220%   $62.4617   $62.46   $62.45   $62.50  
  Purchase #3 $42.74   11.235%   $47.5418   $47.54   $47.55   $47.50  
  Purchase #4 $198.64   6.196%   $210.9477   $210.95   $210.95   $210.90  
  Purchase #5 $31.94   10.478%   $35.2867   $35.29   $35.30   $35.30  
  Purchase #6 $67.49   10.211%   $74.3814   $74.38   $74.40   $74.40  
  Purchase #7 $66.70   9.786%   $73.2273   $73.23   $73.25   $73.20  
  7 purchase totals = $707.15       $773.0063   $773.01   $773.05   $773.00