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 $54.91   11.563%   $61.2592   $61.26   $61.25   $61.30  
  Purchase #2 $212.37   7.295%   $227.8624   $227.86   $227.85   $227.90  
  Purchase #3 $154.57   6.364%   $164.4068   $164.41   $164.40   $164.40  
  Purchase #4 $185.26   10.203%   $204.1621   $204.16   $204.15   $204.20  
  Purchase #5 $131.46   9.828%   $144.3799   $144.38   $144.40   $144.40  
  Purchase #6 $200.27   3.215%   $206.7087   $206.71   $206.70   $206.70  
  Purchase #7 $176.70   11.670%   $197.3209   $197.32   $197.30   $197.30  
  7 purchase totals = $1,115.54       $1,206.1000   $1,206.10   $1,206.05   $1,206.20