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 $39.55   11.631%   $44.1501   $44.15   $44.15   $44.20  
  Purchase #2 $173.66   5.349%   $182.9491   $182.95   $182.95   $182.90  
  Purchase #3 $121.86   9.686%   $133.6634   $133.66   $133.65   $133.70  
  Purchase #4 $177.90   6.225%   $188.9743   $188.97   $188.95   $189.00  
  Purchase #5 $67.69   8.709%   $73.5851   $73.59   $73.60   $73.60  
  Purchase #6 $11.94   5.859%   $12.6396   $12.64   $12.65   $12.60  
  Purchase #7 $249.91   4.845%   $262.0181   $262.02   $262.00   $262.00  
  7 purchase totals = $842.51       $897.9797   $897.98   $897.95   $898.00