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 $194.80   11.678%   $217.5487   $217.55   $217.55   $217.50  
  Purchase #2 $190.40   4.126%   $198.2559   $198.26   $198.25   $198.30  
  Purchase #3 $77.69   10.678%   $85.9857   $85.99   $86.00   $86.00  
  Purchase #4 $182.86   13.678%   $207.8716   $207.87   $207.85   $207.90  
  Purchase #5 $94.90   3.820%   $98.5252   $98.53   $98.55   $98.50  
  Purchase #6 $33.42   4.803%   $35.0252   $35.03   $35.05   $35.00  
  Purchase #7 $94.90   3.783%   $98.4901   $98.49   $98.50   $98.50  
  7 purchase totals = $868.97       $941.7024   $941.72   $941.75   $941.70