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 $241.97   11.197%   $269.0634   $269.06   $269.05   $269.10  
  Purchase #2 $239.40   8.471%   $259.6796   $259.68   $259.70   $259.70  
  Purchase #3 $5.76   11.395%   $6.4164   $6.42   $6.40   $6.40  
  Purchase #4 $61.62   5.834%   $65.2149   $65.21   $65.20   $65.20  
  Purchase #5 $174.39   10.829%   $193.2747   $193.27   $193.25   $193.30  
  Purchase #6 $60.28   9.398%   $65.9451   $65.95   $65.95   $65.90  
  Purchase #7 $11.63   9.549%   $12.7405   $12.74   $12.75   $12.70  
  7 purchase totals = $795.05       $872.3346   $872.33   $872.30   $872.30