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 $206.41   3.122%   $212.8541   $212.85   $212.85   $212.90  
  Purchase #2 $18.28   8.788%   $19.8864   $19.89   $19.90   $19.90  
  Purchase #3 $247.54   11.871%   $276.9255   $276.93   $276.95   $276.90  
  Purchase #4 $231.26   7.509%   $248.6253   $248.63   $248.65   $248.60  
  Purchase #5 $212.91   10.544%   $235.3592   $235.36   $235.35   $235.40  
  Purchase #6 $151.61   4.138%   $157.8836   $157.88   $157.90   $157.90  
  Purchase #7 $58.30   9.428%   $63.7965   $63.80   $63.80   $63.80  
  7 purchase totals = $1,126.31       $1,215.3306   $1,215.34   $1,215.40   $1,215.40