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 $208.90   8.422%   $226.4936   $226.49   $226.50   $226.50  
  Purchase #2 $29.83   7.794%   $32.155   $32.16   $32.15   $32.20  
  Purchase #3 $245.42   8.330%   $265.8635   $265.86   $265.85   $265.90  
  Purchase #4 $198.56   8.127%   $214.697   $214.70   $214.70   $214.70  
  Purchase #5 $184.81   11.577%   $206.2055   $206.21   $206.20   $206.20  
  Purchase #6 $192.59   10.498%   $212.8081   $212.81   $212.80   $212.80  
  Purchase #7 $229.38   6.138%   $243.4593   $243.46   $243.45   $243.50  
  7 purchase totals = $1,289.49       $1,401.6820   $1,401.69   $1,401.65   $1,401.80