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	$20.70	5.343%	$21.806	$21.81	$21.80	$21.80
Purchase #2	$222.42	13.752%	$253.0072	$253.01	$253.00	$253.00
Purchase #3	$52.38	5.708%	$55.3699	$55.37	$55.35	$55.40
Purchase #4	$203.32	10.598%	$224.8679	$224.87	$224.85	$224.90
Purchase #5	$194.80	10.124%	$214.5216	$214.52	$214.50	$214.50
Purchase #6	$82.80	3.712%	$85.8735	$85.87	$85.85	$85.90
Purchase #7	$205.41	7.386%	$220.5816	$220.58	$220.60	$220.60
7 purchase totals =	$981.83		$1,076.0277	$1,076.03	$1,075.95	$1,076.10