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 $59.37   7.242%   $63.6696   $63.67   $63.65   $63.70  
  Purchase #2 $206.62   9.812%   $226.8936   $226.89   $226.90   $226.90  
  Purchase #3 $86.66   13.271%   $98.1606   $98.16   $98.15   $98.20  
  Purchase #4 $14.57   8.114%   $15.7522   $15.75   $15.75   $15.80  
  Purchase #5 $24.92   6.467%   $26.5316   $26.53   $26.55   $26.50  
  Purchase #6 $116.71   7.742%   $125.7457   $125.75   $125.75   $125.70  
  Purchase #7 $54.83   10.505%   $60.5899   $60.59   $60.60   $60.60  
  7 purchase totals = $563.68       $617.3432   $617.34   $617.35   $617.40