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 $153.25   5.173%   $161.1776   $161.18   $161.20   $161.20  
  Purchase #2 $38.98   5.311%   $41.0502   $41.05   $41.05   $41.10  
  Purchase #3 $237.66   10.223%   $261.956   $261.96   $261.95   $262.00  
  Purchase #4 $60.29   12.564%   $67.8648   $67.86   $67.85   $67.90  
  Purchase #5 $114.67   13.805%   $130.5002   $130.50   $130.50   $130.50  
  Purchase #6 $114.42   7.460%   $122.9557   $122.96   $122.95   $123.00  
  Purchase #7 $166.43   4.786%   $174.3953   $174.40   $174.40   $174.40  
  7 purchase totals = $885.70       $959.8998   $959.91   $959.90   $960.10