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 $216.99   13.331%   $245.9169   $245.92   $245.90   $245.90  
  Purchase #2 $215.94   8.311%   $233.8868   $233.89   $233.90   $233.90  
  Purchase #3 $13.39   10.756%   $14.8302   $14.83   $14.85   $14.80  
  Purchase #4 $144.87   12.837%   $163.467   $163.47   $163.45   $163.50  
  Purchase #5 $217.61   3.371%   $224.9456   $224.95   $224.95   $224.90  
  Purchase #6 $244.41   9.722%   $268.1715   $268.17   $268.15   $268.20  
  Purchase #7 $155.32   9.246%   $169.6809   $169.68   $169.70   $169.70  
  7 purchase totals = $1,208.53       $1,320.8989   $1,320.91   $1,320.90   $1,320.90