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 $58.27   13.168%   $65.943   $65.94   $65.95   $65.90  
  Purchase #2 $46.97   9.720%   $51.5355   $51.54   $51.55   $51.50  
  Purchase #3 $239.48   4.376%   $249.9596   $249.96   $249.95   $250.00  
  Purchase #4 $233.78   12.174%   $262.2404   $262.24   $262.25   $262.20  
  Purchase #5 $46.91   7.578%   $50.4648   $50.46   $50.45   $50.50  
  Purchase #6 $55.94   13.451%   $63.4645   $63.46   $63.45   $63.50  
  Purchase #7 $230.87   7.824%   $248.9333   $248.93   $248.95   $248.90  
  7 purchase totals = $912.22       $992.5411   $992.53   $992.55   $992.50