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 $55.92   13.832%   $63.6549   $63.65   $63.65   $63.70  
  Purchase #2 $107.70   6.261%   $114.4431   $114.44   $114.45   $114.40  
  Purchase #3 $76.88   10.414%   $84.8863   $84.89   $84.90   $84.90  
  Purchase #4 $41.80   6.257%   $44.4154   $44.42   $44.40   $44.40  
  Purchase #5 $127.48   12.271%   $143.1231   $143.12   $143.10   $143.10  
  Purchase #6 $70.27   3.870%   $72.9894   $72.99   $73.00   $73.00  
  Purchase #7 $59.27   10.466%   $65.4732   $65.47   $65.45   $65.50  
  7 purchase totals = $539.32       $588.9854   $588.98   $588.95   $589.00