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	$19.29	6.860%	$20.6133	$20.61	$20.60	$20.60
Purchase #2	$226.32	12.111%	$253.7296	$253.73	$253.75	$253.70
Purchase #3	$77.68	10.298%	$85.6795	$85.68	$85.70	$85.70
Purchase #4	$55.67	11.678%	$62.1711	$62.17	$62.15	$62.20
Purchase #5	$187.39	3.262%	$193.5027	$193.50	$193.50	$193.50
Purchase #6	$187.57	4.726%	$196.4346	$196.43	$196.45	$196.40
Purchase #7	$168.96	5.391%	$178.0686	$178.07	$178.05	$178.10
7 purchase totals =	$922.88		$990.1994	$990.19	$990.20	$990.20