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 $54.33   4.613%   $56.8362   $56.84   $56.85   $56.80  
  Purchase #2 $233.51   11.841%   $261.1599   $261.16   $261.15   $261.20  
  Purchase #3 $226.35   6.435%   $240.9156   $240.92   $240.90   $240.90  
  Purchase #4 $134.26   13.367%   $152.2065   $152.21   $152.20   $152.20  
  Purchase #5 $138.67   13.373%   $157.2143   $157.21   $157.20   $157.20  
  Purchase #6 $46.93   5.487%   $49.505   $49.51   $49.50   $49.50  
  Purchase #7 $229.34   8.529%   $248.9004   $248.90   $248.90   $248.90  
  7 purchase totals = $1,063.39       $1,166.7379   $1,166.75   $1,166.70   $1,166.70