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 $243.99   7.263%   $261.711   $261.71   $261.70   $261.70  
  Purchase #2 $192.29   8.288%   $208.227   $208.23   $208.25   $208.20  
  Purchase #3 $216.59   9.278%   $236.6852   $236.69   $236.70   $236.70  
  Purchase #4 $122.68   7.491%   $131.87   $131.87   $131.85   $131.90  
  Purchase #5 $178.57   11.758%   $199.5663   $199.57   $199.55   $199.60  
  Purchase #6 $152.60   4.627%   $159.6608   $159.66   $159.65   $159.70  
  Purchase #7 $71.52   6.131%   $75.9049   $75.90   $75.90   $75.90  
  7 purchase totals = $1,178.24       $1,273.6252   $1,273.63   $1,273.60   $1,273.70