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 $188.52   10.737%   $208.7614   $208.76   $208.75   $208.80  
  Purchase #2 $60.52   5.640%   $63.9333   $63.93   $63.95   $63.90  
  Purchase #3 $24.76   5.389%   $26.0943   $26.09   $26.10   $26.10  
  Purchase #4 $86.89   12.759%   $97.9763   $97.98   $98.00   $98.00  
  Purchase #5 $227.80   4.153%   $237.2605   $237.26   $237.25   $237.30  
  Purchase #6 $133.77   5.273%   $140.8237   $140.82   $140.80   $140.80  
  Purchase #7 $72.51   7.856%   $78.2064   $78.21   $78.20   $78.20  
  7 purchase totals = $794.77       $853.0559   $853.05   $853.05   $853.10