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 $42.33   11.302%   $47.1141   $47.11   $47.10   $47.10  
  Purchase #2 $175.88   10.272%   $193.9464   $193.95   $193.95   $193.90  
  Purchase #3 $165.65   4.271%   $172.7249   $172.72   $172.70   $172.70  
  Purchase #4 $50.63   13.418%   $57.4235   $57.42   $57.40   $57.40  
  Purchase #5 $162.86   4.396%   $170.0193   $170.02   $170.00   $170.00  
  Purchase #6 $93.69   4.563%   $97.9651   $97.97   $97.95   $98.00  
  Purchase #7 $114.93   11.112%   $127.701   $127.70   $127.70   $127.70  
  7 purchase totals = $805.97       $866.8943   $866.89   $866.80   $866.80