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	$16.90	10.267%	$18.6351	$18.64	$18.65	$18.60
Purchase #2	$152.94	13.400%	$173.434	$173.43	$173.45	$173.40
Purchase #3	$223.26	6.144%	$236.9771	$236.98	$237.00	$237.00
Purchase #4	$212.30	8.174%	$229.6534	$229.65	$229.65	$229.70
Purchase #5	$149.41	4.698%	$156.4293	$156.43	$156.45	$156.40
Purchase #6	$39.54	3.423%	$40.8935	$40.89	$40.90	$40.90
Purchase #7	$127.46	11.418%	$142.0134	$142.01	$142.00	$142.00
7 purchase totals =	$921.81		$998.0358	$998.03	$998.10	$998.00