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 $245.81   6.254%   $261.183   $261.18   $261.20   $261.20  
  Purchase #2 $175.77   6.719%   $187.58   $187.58   $187.60   $187.60  
  Purchase #3 $64.81   10.176%   $71.4051   $71.41   $71.40   $71.40  
  Purchase #4 $47.89   12.844%   $54.041   $54.04   $54.05   $54.00  
  Purchase #5 $130.99   13.108%   $148.1602   $148.16   $148.15   $148.20  
  Purchase #6 $232.27   8.514%   $252.0455   $252.05   $252.05   $252.00  
  Purchase #7 $114.70   7.447%   $123.2417   $123.24   $123.25   $123.20  
  7 purchase totals = $1,012.24       $1,097.6565   $1,097.66   $1,097.70   $1,097.60