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 $42.37   12.393%   $47.6209   $47.62   $47.60   $47.60  
  Purchase #2 $97.83   5.873%   $103.5756   $103.58   $103.60   $103.60  
  Purchase #3 $208.83   8.233%   $226.023   $226.02   $226.00   $226.00  
  Purchase #4 $106.34   5.808%   $112.5162   $112.52   $112.50   $112.50  
  Purchase #5 $61.40   5.425%   $64.731   $64.73   $64.75   $64.70  
  Purchase #6 $176.81   3.856%   $183.6278   $183.63   $183.65   $183.60  
  Purchase #7 $67.40   12.856%   $76.0649   $76.06   $76.05   $76.10  
  7 purchase totals = $760.98       $814.1594   $814.16   $814.15   $814.10