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 $184.79   4.662%   $193.4049   $193.40   $193.40   $193.40  
  Purchase #2 $211.46   12.334%   $237.5415   $237.54   $237.55   $237.50  
  Purchase #3 $86.62   3.218%   $89.4074   $89.41   $89.40   $89.40  
  Purchase #4 $82.55   8.422%   $89.5024   $89.50   $89.50   $89.50  
  Purchase #5 $204.54   3.358%   $211.4085   $211.41   $211.40   $211.40  
  Purchase #6 $241.53   4.725%   $252.9423   $252.94   $252.95   $252.90  
  Purchase #7 $190.60   4.509%   $199.1942   $199.19   $199.20   $199.20  
  7 purchase totals = $1,202.09       $1,273.4012   $1,273.39   $1,273.40   $1,273.30