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 $47.93   12.373%   $53.8604   $53.86   $53.85   $53.90  
  Purchase #2 $101.37   13.361%   $114.914   $114.91   $114.90   $114.90  
  Purchase #3 $226.76   3.137%   $233.8735   $233.87   $233.85   $233.90  
  Purchase #4 $223.67   4.165%   $232.9859   $232.99   $233.00   $233.00  
  Purchase #5 $6.71   3.724%   $6.9599   $6.96   $6.95   $7.00  
  Purchase #6 $246.49   6.167%   $261.691   $261.69   $261.70   $261.70  
  Purchase #7 $161.75   12.874%   $182.5737   $182.57   $182.55   $182.60  
  7 purchase totals = $1,014.68       $1,086.8584   $1,086.85   $1,086.80   $1,087.00