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	$89.68	11.329%	$99.8398	$99.84	$99.85	$99.80
Purchase #2	$56.72	6.411%	$60.3563	$60.36	$60.35	$60.40
Purchase #3	$30.70	12.800%	$34.6296	$34.63	$34.65	$34.60
Purchase #4	$59.98	12.429%	$67.4349	$67.43	$67.45	$67.40
Purchase #5	$55.95	3.331%	$57.8137	$57.81	$57.80	$57.80
Purchase #6	$160.76	7.773%	$173.2559	$173.26	$173.25	$173.30
Purchase #7	$127.68	5.379%	$134.5479	$134.55	$134.55	$134.50
7 purchase totals =	$581.47		$627.8781	$627.88	$627.90	$627.80