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	$40.32	5.655%	$42.6001	$42.60	$42.60	$42.60
Purchase #2	$70.65	6.203%	$75.0324	$75.03	$75.05	$75.00
Purchase #3	$19.71	3.522%	$20.4042	$20.40	$20.40	$20.40
Purchase #4	$239.76	10.160%	$264.1196	$264.12	$264.10	$264.10
Purchase #5	$89.53	12.766%	$100.9594	$100.96	$100.95	$101.00
Purchase #6	$31.33	9.761%	$34.3881	$34.39	$34.40	$34.40
Purchase #7	$37.32	10.254%	$41.1468	$41.15	$41.15	$41.10
7 purchase totals =	$528.62		$578.6506	$578.65	$578.65	$578.60