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	$127.66	12.649%	$143.8077	$143.81	$143.80	$143.80
Purchase #2	$244.41	8.211%	$264.4785	$264.48	$264.50	$264.50
Purchase #3	$198.43	13.506%	$225.23	$225.23	$225.25	$225.20
Purchase #4	$164.66	11.274%	$183.2238	$183.22	$183.20	$183.20
Purchase #5	$153.92	11.580%	$171.7439	$171.74	$171.75	$171.70
Purchase #6	$132.26	8.591%	$143.6225	$143.62	$143.60	$143.60
Purchase #7	$56.91	12.567%	$64.0619	$64.06	$64.05	$64.10
7 purchase totals =	$1,078.25		$1,196.1683	$1,196.16	$1,196.15	$1,196.10