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 $60.44   8.806%   $65.7623   $65.76   $65.75   $65.80  
  Purchase #2 $43.41   10.316%   $47.8882   $47.89   $47.90   $47.90  
  Purchase #3 $133.93   7.683%   $144.2198   $144.22   $144.20   $144.20  
  Purchase #4 $214.82   4.690%   $224.8951   $224.90   $224.90   $224.90  
  Purchase #5 $106.52   4.382%   $111.1877   $111.19   $111.20   $111.20  
  Purchase #6 $122.38   3.294%   $126.4112   $126.41   $126.40   $126.40  
  Purchase #7 $45.60   6.617%   $48.6174   $48.62   $48.60   $48.60  
  7 purchase totals = $727.10       $768.9817   $768.99   $768.95   $769.00