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	$173.43	3.164%	$178.9173	$178.92	$178.90	$178.90
Purchase #2	$83.88	13.624%	$95.3078	$95.31	$95.30	$95.30
Purchase #3	$121.27	5.318%	$127.7191	$127.72	$127.70	$127.70
Purchase #4	$239.39	4.431%	$249.9974	$250.00	$250.00	$250.00
Purchase #5	$241.65	5.557%	$255.0785	$255.08	$255.10	$255.10
Purchase #6	$133.52	5.142%	$140.3856	$140.39	$140.40	$140.40
Purchase #7	$249.44	12.562%	$280.7747	$280.77	$280.75	$280.80
7 purchase totals =	$1,242.58		$1,328.1804	$1,328.19	$1,328.15	$1,328.20