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 $68.32   7.805%   $73.6524   $73.65   $73.65   $73.70  
  Purchase #2 $119.72   13.522%   $135.9085   $135.91   $135.90   $135.90  
  Purchase #3 $199.69   5.652%   $210.9765   $210.98   $211.00   $211.00  
  Purchase #4 $16.82   5.522%   $17.7488   $17.75   $17.75   $17.70  
  Purchase #5 $35.36   8.249%   $38.2768   $38.28   $38.30   $38.30  
  Purchase #6 $132.82   4.423%   $138.6946   $138.69   $138.70   $138.70  
  Purchase #7 $248.50   13.343%   $281.6574   $281.66   $281.65   $281.70  
  7 purchase totals = $821.23       $896.9150   $896.92   $896.95   $897.00