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 $24.31   8.815%   $26.4529   $26.45   $26.45   $26.50  
  Purchase #2 $172.83   13.552%   $196.2519   $196.25   $196.25   $196.30  
  Purchase #3 $237.81   3.328%   $245.7243   $245.72   $245.70   $245.70  
  Purchase #4 $183.87   3.599%   $190.4875   $190.49   $190.50   $190.50  
  Purchase #5 $13.50   10.719%   $14.9471   $14.95   $14.95   $14.90  
  Purchase #6 $149.97   4.743%   $157.0831   $157.08   $157.10   $157.10  
  Purchase #7 $241.70   10.585%   $267.2839   $267.28   $267.30   $267.30  
  7 purchase totals = $1,023.99       $1,098.2307   $1,098.22   $1,098.25   $1,098.30