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	$9.56	11.599%	$10.6689	$10.67	$10.65	$10.70
Purchase #2	$129.32	8.405%	$140.1893	$140.19	$140.20	$140.20
Purchase #3	$78.58	12.658%	$88.5267	$88.53	$88.55	$88.50
Purchase #4	$18.45	7.149%	$19.769	$19.77	$19.75	$19.80
Purchase #5	$55.78	11.352%	$62.1121	$62.11	$62.10	$62.10
Purchase #6	$70.43	10.106%	$77.5477	$77.55	$77.55	$77.50
Purchase #7	$39.70	13.346%	$44.9984	$45.00	$45.00	$45.00
7 purchase totals =	$401.82		$443.8121	$443.82	$443.80	$443.80