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	$6.56	9.686%	$7.1954	$7.20	$7.20	$7.20
Purchase #2	$93.80	7.523%	$100.8566	$100.86	$100.85	$100.90
Purchase #3	$161.94	3.144%	$167.0314	$167.03	$167.05	$167.00
Purchase #4	$114.96	11.103%	$127.724	$127.72	$127.70	$127.70
Purchase #5	$105.58	13.782%	$120.131	$120.13	$120.15	$120.10
Purchase #6	$97.44	7.574%	$104.8201	$104.82	$104.80	$104.80
Purchase #7	$178.86	4.685%	$187.2396	$187.24	$187.25	$187.20
7 purchase totals =	$759.14		$814.9981	$815.00	$815.00	$814.90