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 $205.32   5.565%   $216.7461   $216.75   $216.75   $216.70  
  Purchase #2 $155.51   8.648%   $168.9585   $168.96   $168.95   $169.00  
  Purchase #3 $179.83   3.265%   $185.7014   $185.70   $185.70   $185.70  
  Purchase #4 $121.41   8.125%   $131.2746   $131.27   $131.25   $131.30  
  Purchase #5 $212.75   7.106%   $227.868   $227.87   $227.85   $227.90  
  Purchase #6 $49.91   5.626%   $52.7179   $52.72   $52.70   $52.70  
  Purchase #7 $248.64   12.799%   $280.4634   $280.46   $280.45   $280.50  
  7 purchase totals = $1,173.37       $1,263.7299   $1,263.73   $1,263.65   $1,263.80