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	$12.76	12.117%	$14.3061	$14.31	$14.30	$14.30
Purchase #2	$189.42	8.565%	$205.6438	$205.64	$205.65	$205.60
Purchase #3	$124.25	10.511%	$137.3099	$137.31	$137.30	$137.30
Purchase #4	$100.33	10.638%	$111.0031	$111.00	$111.00	$111.00
Purchase #5	$147.31	4.103%	$153.3541	$153.35	$153.35	$153.40
Purchase #6	$33.87	5.655%	$35.7853	$35.79	$35.80	$35.80
Purchase #7	$167.92	4.492%	$175.463	$175.46	$175.45	$175.50
7 purchase totals =	$775.86		$832.8653	$832.86	$832.85	$832.90