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 $87.71   12.102%   $98.3247   $98.32   $98.30   $98.30  
  Purchase #2 $119.64   9.213%   $130.6624   $130.66   $130.65   $130.70  
  Purchase #3 $119.91   6.544%   $127.7569   $127.76   $127.75   $127.80  
  Purchase #4 $101.42   13.635%   $115.2486   $115.25   $115.25   $115.20  
  Purchase #5 $82.60   12.263%   $92.7292   $92.73   $92.75   $92.70  
  Purchase #6 $176.43   4.383%   $184.1629   $184.16   $184.15   $184.20  
  Purchase #7 $97.46   10.567%   $107.7586   $107.76   $107.75   $107.80  
  7 purchase totals = $785.17       $856.6433   $856.64   $856.60   $856.70