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 $248.89   7.856%   $268.4428   $268.44   $268.45   $268.40  
  Purchase #2 $99.66   6.199%   $105.8379   $105.84   $105.85   $105.80  
  Purchase #3 $26.57   7.583%   $28.5848   $28.58   $28.60   $28.60  
  Purchase #4 $214.25   10.805%   $237.3997   $237.40   $237.40   $237.40  
  Purchase #5 $16.51   3.598%   $17.104   $17.10   $17.10   $17.10  
  Purchase #6 $152.40   3.633%   $157.9367   $157.94   $157.95   $157.90  
  Purchase #7 $185.41   3.850%   $192.5483   $192.55   $192.55   $192.50  
  7 purchase totals = $943.69       $1,007.8542   $1,007.85   $1,007.90   $1,007.70