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 $66.92   9.655%   $73.3811   $73.38   $73.40   $73.40  
  Purchase #2 $197.75   4.521%   $206.6903   $206.69   $206.70   $206.70  
  Purchase #3 $176.47   7.746%   $190.1394   $190.14   $190.15   $190.10  
  Purchase #4 $127.69   3.316%   $131.9242   $131.92   $131.90   $131.90  
  Purchase #5 $135.42   6.567%   $144.313   $144.31   $144.30   $144.30  
  Purchase #6 $22.47   4.374%   $23.4528   $23.45   $23.45   $23.50  
  Purchase #7 $166.84   8.222%   $180.5576   $180.56   $180.55   $180.60  
  7 purchase totals = $893.56       $950.4584   $950.45   $950.45   $950.50