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 $222.51   11.184%   $247.3955   $247.40   $247.40   $247.40  
  Purchase #2 $106.51   9.126%   $116.2301   $116.23   $116.25   $116.20  
  Purchase #3 $163.78   11.167%   $182.0693   $182.07   $182.05   $182.10  
  Purchase #4 $224.81   9.704%   $246.6256   $246.63   $246.65   $246.60  
  Purchase #5 $214.62   12.387%   $241.205   $241.21   $241.20   $241.20  
  Purchase #6 $136.42   6.133%   $144.7866   $144.79   $144.80   $144.80  
  Purchase #7 $76.34   7.739%   $82.248   $82.25   $82.25   $82.20  
  7 purchase totals = $1,144.99       $1,260.5601   $1,260.58   $1,260.60   $1,260.50