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 $199.69   3.573%   $206.8249   $206.82   $206.80   $206.80  
  Purchase #2 $101.73   12.828%   $114.7799   $114.78   $114.80   $114.80  
  Purchase #3 $24.32   9.316%   $26.5857   $26.59   $26.60   $26.60  
  Purchase #4 $203.28   7.635%   $218.8004   $218.80   $218.80   $218.80  
  Purchase #5 $61.25   4.253%   $63.855   $63.86   $63.85   $63.90  
  Purchase #6 $241.51   3.641%   $250.3034   $250.30   $250.30   $250.30  
  Purchase #7 $50.76   9.515%   $55.5898   $55.59   $55.60   $55.60  
  7 purchase totals = $882.54       $936.7391   $936.74   $936.75   $936.80