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 $239.53   11.128%   $266.1849   $266.18   $266.20   $266.20  
  Purchase #2 $151.64   11.205%   $168.6313   $168.63   $168.65   $168.60  
  Purchase #3 $78.99   10.860%   $87.5683   $87.57   $87.55   $87.60  
  Purchase #4 $22.90   8.717%   $24.8962   $24.90   $24.90   $24.90  
  Purchase #5 $180.81   5.284%   $190.364   $190.36   $190.35   $190.40  
  Purchase #6 $240.37   5.291%   $253.088   $253.09   $253.10   $253.10  
  Purchase #7 $225.90   12.761%   $254.7271   $254.73   $254.75   $254.70  
  7 purchase totals = $1,140.14       $1,245.4598   $1,245.46   $1,245.50   $1,245.50