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	$34.89	13.339%	$39.544	$39.54	$39.55	$39.50
Purchase #2	$228.81	11.557%	$255.2536	$255.25	$255.25	$255.30
Purchase #3	$230.81	3.195%	$238.1844	$238.18	$238.20	$238.20
Purchase #4	$54.33	9.321%	$59.3941	$59.39	$59.40	$59.40
Purchase #5	$115.87	6.726%	$123.6634	$123.66	$123.65	$123.70
Purchase #6	$7.25	12.218%	$8.1358	$8.14	$8.15	$8.10
Purchase #7	$118.80	10.131%	$130.8356	$130.84	$130.85	$130.80
7 purchase totals =	$790.76		$855.0109	$855.00	$855.05	$855.00