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 $86.75   8.278%   $93.9312   $93.93   $93.95   $93.90  
  Purchase #2 $95.36   3.411%   $98.6127   $98.61   $98.60   $98.60  
  Purchase #3 $65.78   8.206%   $71.1779   $71.18   $71.20   $71.20  
  Purchase #4 $59.66   5.856%   $63.1537   $63.15   $63.15   $63.20  
  Purchase #5 $215.54   12.395%   $242.2562   $242.26   $242.25   $242.30  
  Purchase #6 $93.50   9.499%   $102.3816   $102.38   $102.40   $102.40  
  Purchase #7 $74.28   5.725%   $78.5325   $78.53   $78.55   $78.50  
  7 purchase totals = $690.87       $750.0458   $750.04   $750.10   $750.10