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 $245.60   6.613%   $261.8415   $261.84   $261.85   $261.80  
  Purchase #2 $168.76   11.564%   $188.2754   $188.28   $188.30   $188.30  
  Purchase #3 $206.91   9.666%   $226.9099   $226.91   $226.90   $226.90  
  Purchase #4 $101.44   12.866%   $114.4913   $114.49   $114.50   $114.50  
  Purchase #5 $36.62   9.821%   $40.2165   $40.22   $40.20   $40.20  
  Purchase #6 $103.92   6.655%   $110.8359   $110.84   $110.85   $110.80  
  Purchase #7 $149.42   3.183%   $154.176   $154.18   $154.20   $154.20  
  7 purchase totals = $1,012.67       $1,096.7465   $1,096.76   $1,096.80   $1,096.70