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 $241.56   11.624%   $269.6389   $269.64   $269.65   $269.60  
  Purchase #2 $151.71   9.496%   $166.1164   $166.12   $166.10   $166.10  
  Purchase #3 $130.80   4.341%   $136.478   $136.48   $136.50   $136.50  
  Purchase #4 $222.32   3.162%   $229.3498   $229.35   $229.35   $229.30  
  Purchase #5 $248.27   5.667%   $262.3395   $262.34   $262.35   $262.30  
  Purchase #6 $231.84   10.725%   $256.7048   $256.70   $256.70   $256.70  
  Purchase #7 $249.41   12.275%   $280.0251   $280.03   $280.05   $280.00  
  7 purchase totals = $1,475.91       $1,600.6525   $1,600.66   $1,600.70   $1,600.50