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	$122.80	8.807%	$133.615	$133.62	$133.60	$133.60
Purchase #2	$158.87	10.540%	$175.6149	$175.61	$175.60	$175.60
Purchase #3	$223.83	4.137%	$233.0898	$233.09	$233.10	$233.10
Purchase #4	$52.38	6.185%	$55.6197	$55.62	$55.60	$55.60
Purchase #5	$101.26	4.204%	$105.517	$105.52	$105.50	$105.50
Purchase #6	$92.60	3.308%	$95.6632	$95.66	$95.65	$95.70
Purchase #7	$48.61	4.328%	$50.7138	$50.71	$50.70	$50.70
7 purchase totals =	$800.35		$849.8334	$849.83	$849.75	$849.80