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 $228.76   11.447%   $254.9462   $254.95   $254.95   $254.90  
  Purchase #2 $215.60   5.583%   $227.6369   $227.64   $227.65   $227.60  
  Purchase #3 $56.93   10.772%   $63.0625   $63.06   $63.05   $63.10  
  Purchase #4 $65.30   12.601%   $73.5285   $73.53   $73.55   $73.50  
  Purchase #5 $160.68   8.166%   $173.8011   $173.80   $173.80   $173.80  
  Purchase #6 $116.32   8.622%   $126.3491   $126.35   $126.35   $126.30  
  Purchase #7 $143.48   12.624%   $161.5929   $161.59   $161.60   $161.60  
  7 purchase totals = $987.07       $1,080.9172   $1,080.92   $1,080.95   $1,080.80