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 $85.69   8.328%   $92.8263   $92.83   $92.85   $92.80  
  Purchase #2 $47.83   7.433%   $51.3852   $51.39   $51.40   $51.40  
  Purchase #3 $132.62   8.354%   $143.6991   $143.70   $143.70   $143.70  
  Purchase #4 $198.68   13.871%   $226.2389   $226.24   $226.25   $226.20  
  Purchase #5 $47.25   4.836%   $49.535   $49.54   $49.55   $49.50  
  Purchase #6 $182.88   13.141%   $206.9123   $206.91   $206.90   $206.90  
  Purchase #7 $179.61   5.491%   $189.4724   $189.47   $189.45   $189.50  
  7 purchase totals = $874.56       $960.0692   $960.08   $960.10   $960.00