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 $233.99   11.643%   $261.2335   $261.23   $261.25   $261.20  
  Purchase #2 $227.68   9.316%   $248.8907   $248.89   $248.90   $248.90  
  Purchase #3 $162.86   6.558%   $173.5404   $173.54   $173.55   $173.50  
  Purchase #4 $152.32   7.274%   $163.3998   $163.40   $163.40   $163.40  
  Purchase #5 $157.69   11.814%   $176.3195   $176.32   $176.30   $176.30  
  Purchase #6 $26.33   5.163%   $27.6894   $27.69   $27.70   $27.70  
  Purchase #7 $68.80   9.833%   $75.5651   $75.57   $75.55   $75.60  
  7 purchase totals = $1,029.67       $1,126.6384   $1,126.64   $1,126.65   $1,126.60