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 $56.57   4.733%   $59.2475   $59.25   $59.25   $59.20  
  Purchase #2 $115.60   8.868%   $125.8514   $125.85   $125.85   $125.90  
  Purchase #3 $50.44   12.102%   $56.5442   $56.54   $56.55   $56.50  
  Purchase #4 $39.44   10.484%   $43.5749   $43.57   $43.55   $43.60  
  Purchase #5 $81.73   6.533%   $87.0694   $87.07   $87.05   $87.10  
  Purchase #6 $227.55   9.209%   $248.5051   $248.51   $248.50   $248.50  
  Purchase #7 $153.87   5.534%   $162.3852   $162.39   $162.40   $162.40  
  7 purchase totals = $725.20       $783.1777   $783.18   $783.15   $783.20