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	$54.50	9.255%	$59.544	$59.54	$59.55	$59.50
Purchase #2	$39.66	4.721%	$41.5323	$41.53	$41.55	$41.50
Purchase #3	$48.64	10.211%	$53.6066	$53.61	$53.60	$53.60
Purchase #4	$7.70	5.615%	$8.1324	$8.13	$8.15	$8.10
Purchase #5	$44.98	6.345%	$47.834	$47.83	$47.85	$47.80
Purchase #6	$73.81	5.343%	$77.7537	$77.75	$77.75	$77.80
Purchase #7	$19.27	4.296%	$20.0978	$20.10	$20.10	$20.10
7 purchase totals =	$288.56		$308.5008	$308.49	$308.55	$308.40