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	$239.75	10.372%	$264.6169	$264.62	$264.60	$264.60
Purchase #2	$54.29	8.717%	$59.0225	$59.02	$59.00	$59.00
Purchase #3	$60.75	9.328%	$66.4168	$66.42	$66.40	$66.40
Purchase #4	$234.54	5.234%	$246.8158	$246.82	$246.80	$246.80
Purchase #5	$223.87	6.327%	$238.0343	$238.03	$238.05	$238.00
Purchase #6	$57.45	9.533%	$62.9267	$62.93	$62.95	$62.90
Purchase #7	$60.97	6.354%	$64.844	$64.84	$64.85	$64.80
7 purchase totals =	$931.62		$1,002.6770	$1,002.68	$1,002.65	$1,002.50