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 $229.70   13.609%   $260.9599   $260.96   $260.95   $261.00  
  Purchase #2 $149.75   10.520%   $165.5037   $165.50   $165.50   $165.50  
  Purchase #3 $176.97   3.110%   $182.4738   $182.47   $182.45   $182.50  
  Purchase #4 $54.34   6.247%   $57.7346   $57.73   $57.75   $57.70  
  Purchase #5 $160.31   10.548%   $177.2195   $177.22   $177.20   $177.20  
  Purchase #6 $141.81   3.529%   $146.8145   $146.81   $146.80   $146.80  
  Purchase #7 $130.51   11.729%   $145.8175   $145.82   $145.80   $145.80  
  7 purchase totals = $1,043.39       $1,136.5235   $1,136.51   $1,136.45   $1,136.50