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	$142.89	11.197%	$158.8894	$158.89	$158.90	$158.90
Purchase #2	$97.93	13.447%	$111.0986	$111.10	$111.10	$111.10
Purchase #3	$92.44	12.570%	$104.0597	$104.06	$104.05	$104.10
Purchase #4	$52.68	12.500%	$59.265	$59.27	$59.25	$59.30
Purchase #5	$85.49	12.321%	$96.0232	$96.02	$96.00	$96.00
Purchase #6	$175.64	10.263%	$193.6659	$193.67	$193.65	$193.70
Purchase #7	$85.54	9.602%	$93.7536	$93.75	$93.75	$93.80
7 purchase totals =	$732.61		$816.7554	$816.76	$816.70	$816.90