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	$207.42	11.164%	$230.5764	$230.58	$230.60	$230.60
Purchase #2	$163.64	5.577%	$172.7662	$172.77	$172.75	$172.80
Purchase #3	$56.32	5.588%	$59.4672	$59.47	$59.45	$59.50
Purchase #4	$57.44	4.370%	$59.9501	$59.95	$59.95	$60.00
Purchase #5	$21.38	3.169%	$22.0575	$22.06	$22.05	$22.10
Purchase #6	$68.84	3.535%	$71.2735	$71.27	$71.25	$71.30
Purchase #7	$46.93	6.169%	$49.8251	$49.83	$49.85	$49.80
7 purchase totals =	$621.97		$665.9160	$665.93	$665.90	$666.10