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 $60.87   3.407%   $62.9438   $62.94   $62.95   $62.90  
  Purchase #2 $224.38   6.545%   $239.0657   $239.07   $239.05   $239.10  
  Purchase #3 $153.81   10.436%   $169.8616   $169.86   $169.85   $169.90  
  Purchase #4 $186.30   9.333%   $203.6874   $203.69   $203.70   $203.70  
  Purchase #5 $193.89   7.746%   $208.9087   $208.91   $208.90   $208.90  
  Purchase #6 $239.68   4.346%   $250.0965   $250.10   $250.10   $250.10  
  Purchase #7 $146.94   11.382%   $163.6647   $163.66   $163.65   $163.70  
  7 purchase totals = $1,205.87       $1,298.2284   $1,298.23   $1,298.20   $1,298.30