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 $213.30   5.312%   $224.6305   $224.63   $224.65   $224.60  
  Purchase #2 $185.31   3.856%   $192.4556   $192.46   $192.45   $192.50  
  Purchase #3 $90.82   4.861%   $95.2348   $95.23   $95.25   $95.20  
  Purchase #4 $34.74   3.724%   $36.0337   $36.03   $36.05   $36.00  
  Purchase #5 $125.33   5.762%   $132.5515   $132.55   $132.55   $132.60  
  Purchase #6 $5.36   5.240%   $5.6409   $5.64   $5.65   $5.60  
  Purchase #7 $185.80   5.738%   $196.4612   $196.46   $196.45   $196.50  
  7 purchase totals = $840.66       $883.0082   $883.00   $883.05   $883.00