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 $218.59   10.814%   $242.2283   $242.23   $242.25   $242.20  
  Purchase #2 $183.62   3.686%   $190.3882   $190.39   $190.40   $190.40  
  Purchase #3 $169.73   3.831%   $176.2324   $176.23   $176.25   $176.20  
  Purchase #4 $62.76   6.355%   $66.7484   $66.75   $66.75   $66.70  
  Purchase #5 $8.27   8.524%   $8.9749   $8.97   $8.95   $9.00  
  Purchase #6 $239.33   5.291%   $251.993   $251.99   $252.00   $252.00  
  Purchase #7 $147.61   9.386%   $161.4647   $161.46   $161.45   $161.50  
  7 purchase totals = $1,029.91       $1,098.0299   $1,098.02   $1,098.05   $1,098.00