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	$120.28	12.472%	$135.2813	$135.28	$135.30	$135.30
Purchase #2	$246.72	3.390%	$255.0838	$255.08	$255.10	$255.10
Purchase #3	$226.42	12.719%	$255.2184	$255.22	$255.20	$255.20
Purchase #4	$93.80	7.447%	$100.7853	$100.79	$100.80	$100.80
Purchase #5	$249.34	13.109%	$282.026	$282.03	$282.05	$282.00
Purchase #6	$69.31	13.213%	$78.4679	$78.47	$78.45	$78.50
Purchase #7	$96.49	8.531%	$104.7216	$104.72	$104.70	$104.70
7 purchase totals =	$1,102.36		$1,211.5843	$1,211.59	$1,211.60	$1,211.60