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 $94.89   3.861%   $98.5537   $98.55   $98.55   $98.60  
  Purchase #2 $227.72   6.232%   $241.9115   $241.91   $241.90   $241.90  
  Purchase #3 $48.62   4.633%   $50.8726   $50.87   $50.85   $50.90  
  Purchase #4 $66.62   6.175%   $70.7338   $70.73   $70.75   $70.70  
  Purchase #5 $122.80   5.600%   $129.6768   $129.68   $129.70   $129.70  
  Purchase #6 $124.50   4.475%   $130.0714   $130.07   $130.05   $130.10  
  Purchase #7 $180.82   5.370%   $190.53   $190.53   $190.55   $190.50  
  7 purchase totals = $865.97       $912.3498   $912.34   $912.35   $912.40