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 $237.51   13.460%   $269.4788   $269.48   $269.50   $269.50  
  Purchase #2 $131.76   9.524%   $144.3088   $144.31   $144.30   $144.30  
  Purchase #3 $215.32   5.754%   $227.7095   $227.71   $227.70   $227.70  
  Purchase #4 $196.58   6.106%   $208.5832   $208.58   $208.60   $208.60  
  Purchase #5 $96.62   11.665%   $107.8907   $107.89   $107.90   $107.90  
  Purchase #6 $206.55   3.658%   $214.1056   $214.11   $214.10   $214.10  
  Purchase #7 $199.84   11.541%   $222.9035   $222.90   $222.90   $222.90  
  7 purchase totals = $1,284.18       $1,394.9801   $1,394.98   $1,395.00   $1,395.00