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 $52.28   5.587%   $55.2009   $55.20   $55.20   $55.20  
  Purchase #2 $106.61   7.593%   $114.7049   $114.70   $114.70   $114.70  
  Purchase #3 $11.73   9.859%   $12.8865   $12.89   $12.90   $12.90  
  Purchase #4 $25.53   8.543%   $27.711   $27.71   $27.70   $27.70  
  Purchase #5 $25.93   5.491%   $27.3538   $27.35   $27.35   $27.40  
  Purchase #6 $59.94   3.669%   $62.1392   $62.14   $62.15   $62.10  
  Purchase #7 $201.32   4.720%   $210.8223   $210.82   $210.80   $210.80  
  7 purchase totals = $483.34       $510.8186   $510.81   $510.80   $510.80