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 $225.34   7.174%   $241.5059   $241.51   $241.50   $241.50  
  Purchase #2 $114.53   13.175%   $129.6193   $129.62   $129.60   $129.60  
  Purchase #3 $34.42   4.387%   $35.93   $35.93   $35.95   $35.90  
  Purchase #4 $176.99   3.356%   $182.9298   $182.93   $182.95   $182.90  
  Purchase #5 $67.89   11.866%   $75.9458   $75.95   $75.95   $75.90  
  Purchase #6 $175.82   5.170%   $184.9099   $184.91   $184.90   $184.90  
  Purchase #7 $52.58   9.566%   $57.6098   $57.61   $57.60   $57.60  
  7 purchase totals = $847.57       $908.4505   $908.46   $908.45   $908.30