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 $74.59   11.482%   $83.1544   $83.15   $83.15   $83.20  
  Purchase #2 $173.83   13.567%   $197.4135   $197.41   $197.40   $197.40  
  Purchase #3 $192.34   3.779%   $199.6085   $199.61   $199.60   $199.60  
  Purchase #4 $214.40   5.830%   $226.8995   $226.90   $226.90   $226.90  
  Purchase #5 $168.87   9.616%   $185.1085   $185.11   $185.10   $185.10  
  Purchase #6 $162.83   13.558%   $184.9065   $184.91   $184.90   $184.90  
  Purchase #7 $193.56   4.318%   $201.9179   $201.92   $201.90   $201.90  
  7 purchase totals = $1,180.42       $1,279.0088   $1,279.01   $1,278.95   $1,279.00