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 $201.46   6.754%   $215.0666   $215.07   $215.05   $215.10  
  Purchase #2 $90.76   8.776%   $98.7251   $98.73   $98.75   $98.70  
  Purchase #3 $86.93   7.419%   $93.3793   $93.38   $93.40   $93.40  
  Purchase #4 $61.57   13.591%   $69.938   $69.94   $69.95   $69.90  
  Purchase #5 $211.73   12.643%   $238.499   $238.50   $238.50   $238.50  
  Purchase #6 $86.61   6.405%   $92.1574   $92.16   $92.15   $92.20  
  Purchase #7 $208.91   3.510%   $216.2427   $216.24   $216.25   $216.20  
  7 purchase totals = $947.97       $1,024.0081   $1,024.02   $1,024.05   $1,024.00