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 $56.72   5.702%   $59.9542   $59.95   $59.95   $60.00  
  Purchase #2 $43.62   13.685%   $49.5894   $49.59   $49.60   $49.60  
  Purchase #3 $249.47   11.523%   $278.2164   $278.22   $278.20   $278.20  
  Purchase #4 $248.75   8.315%   $269.4336   $269.43   $269.45   $269.40  
  Purchase #5 $190.79   9.268%   $208.4724   $208.47   $208.45   $208.50  
  Purchase #6 $129.63   11.872%   $145.0197   $145.02   $145.00   $145.00  
  Purchase #7 $240.62   7.773%   $259.3234   $259.32   $259.30   $259.30  
  7 purchase totals = $1,159.60       $1,270.0091   $1,270.00   $1,269.95   $1,270.00