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 $84.37   13.781%   $95.997   $96.00   $96.00   $96.00  
  Purchase #2 $169.68   10.777%   $187.9664   $187.97   $187.95   $188.00  
  Purchase #3 $216.71   10.589%   $239.6574   $239.66   $239.65   $239.70  
  Purchase #4 $177.63   8.580%   $192.8707   $192.87   $192.85   $192.90  
  Purchase #5 $157.25   5.275%   $165.5449   $165.54   $165.55   $165.50  
  Purchase #6 $29.61   3.642%   $30.6884   $30.69   $30.70   $30.70  
  Purchase #7 $24.27   8.845%   $26.4167   $26.42   $26.40   $26.40  
  7 purchase totals = $859.52       $939.1415   $939.15   $939.10   $939.20