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 $58.27   13.419%   $66.0893   $66.09   $66.10   $66.10  
  Purchase #2 $142.68   8.513%   $154.8263   $154.83   $154.85   $154.80  
  Purchase #3 $52.64   6.481%   $56.0516   $56.05   $56.05   $56.10  
  Purchase #4 $214.74   5.557%   $226.6731   $226.67   $226.65   $226.70  
  Purchase #5 $160.51   8.610%   $174.3299   $174.33   $174.35   $174.30  
  Purchase #6 $73.73   10.157%   $81.2188   $81.22   $81.20   $81.20  
  Purchase #7 $188.59   4.537%   $197.1463   $197.15   $197.15   $197.10  
  7 purchase totals = $891.16       $956.3353   $956.34   $956.35   $956.30