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	$48.26	8.111%	$52.1744	$52.17	$52.15	$52.20
Purchase #2	$66.59	13.328%	$75.4651	$75.47	$75.45	$75.50
Purchase #3	$196.69	13.765%	$223.7644	$223.76	$223.75	$223.80
Purchase #4	$107.81	3.496%	$111.579	$111.58	$111.60	$111.60
Purchase #5	$43.84	12.674%	$49.3963	$49.40	$49.40	$49.40
Purchase #6	$14.39	7.534%	$15.4741	$15.47	$15.45	$15.50
Purchase #7	$101.28	11.201%	$112.6244	$112.62	$112.60	$112.60
7 purchase totals =	$578.86		$640.4777	$640.47	$640.40	$640.60