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	$29.37	10.318%	$32.4004	$32.40	$32.40	$32.40
Purchase #2	$52.87	3.303%	$54.6163	$54.62	$54.60	$54.60
Purchase #3	$182.91	6.329%	$194.4864	$194.49	$194.50	$194.50
Purchase #4	$34.51	4.347%	$36.0101	$36.01	$36.00	$36.00
Purchase #5	$192.28	4.154%	$200.2673	$200.27	$200.25	$200.30
Purchase #6	$155.64	11.426%	$173.4234	$173.42	$173.40	$173.40
Purchase #7	$127.55	12.707%	$143.7578	$143.76	$143.75	$143.80
7 purchase totals =	$775.13		$834.9617	$834.97	$834.90	$835.00