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	$79.71	12.523%	$89.6921	$89.69	$89.70	$89.70
Purchase #2	$34.72	12.509%	$39.0631	$39.06	$39.05	$39.10
Purchase #3	$40.31	9.403%	$44.1003	$44.10	$44.10	$44.10
Purchase #4	$124.36	5.757%	$131.5194	$131.52	$131.50	$131.50
Purchase #5	$111.51	6.559%	$118.8239	$118.82	$118.80	$118.80
Purchase #6	$159.96	6.443%	$170.2662	$170.27	$170.25	$170.30
Purchase #7	$186.36	7.489%	$200.3165	$200.32	$200.30	$200.30
7 purchase totals =	$736.93		$793.7815	$793.78	$793.70	$793.80