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 $62.63   8.834%   $68.1627   $68.16   $68.15   $68.20  
  Purchase #2 $229.72   13.811%   $261.4466   $261.45   $261.45   $261.40  
  Purchase #3 $207.30   3.468%   $214.4892   $214.49   $214.50   $214.50  
  Purchase #4 $17.50   3.558%   $18.1227   $18.12   $18.10   $18.10  
  Purchase #5 $83.74   11.814%   $93.633   $93.63   $93.65   $93.60  
  Purchase #6 $35.53   13.520%   $40.3337   $40.33   $40.35   $40.30  
  Purchase #7 $103.60   10.856%   $114.8468   $114.85   $114.85   $114.80  
  7 purchase totals = $740.02       $811.0347   $811.03   $811.05   $810.90