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 $70.62   4.222%   $73.6016   $73.60   $73.60   $73.60  
  Purchase #2 $83.61   11.699%   $93.3915   $93.39   $93.40   $93.40  
  Purchase #3 $177.38   13.705%   $201.6899   $201.69   $201.70   $201.70  
  Purchase #4 $71.78   11.520%   $80.0491   $80.05   $80.05   $80.00  
  Purchase #5 $135.42   11.423%   $150.889   $150.89   $150.90   $150.90  
  Purchase #6 $70.28   3.309%   $72.6056   $72.61   $72.60   $72.60  
  Purchase #7 $67.78   13.854%   $77.1702   $77.17   $77.15   $77.20  
  7 purchase totals = $676.87       $749.3969   $749.40   $749.40   $749.40