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 $207.83   9.131%   $226.807   $226.81   $226.80   $226.80  
  Purchase #2 $164.45   13.539%   $186.7149   $186.71   $186.70   $186.70  
  Purchase #3 $22.70   8.320%   $24.5886   $24.59   $24.60   $24.60  
  Purchase #4 $9.64   5.336%   $10.1544   $10.15   $10.15   $10.20  
  Purchase #5 $228.32   3.763%   $236.9117   $236.91   $236.90   $236.90  
  Purchase #6 $175.66   8.569%   $190.7123   $190.71   $190.70   $190.70  
  Purchase #7 $131.76   12.785%   $148.6055   $148.61   $148.60   $148.60  
  7 purchase totals = $940.36       $1,024.4944   $1,024.49   $1,024.45   $1,024.50