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	$159.82	3.670%	$165.6854	$165.69	$165.70	$165.70
Purchase #2	$124.46	12.539%	$140.066	$140.07	$140.05	$140.10
Purchase #3	$63.98	9.604%	$70.1246	$70.12	$70.10	$70.10
Purchase #4	$35.64	5.565%	$37.6234	$37.62	$37.60	$37.60
Purchase #5	$11.45	3.692%	$11.8727	$11.87	$11.85	$11.90
Purchase #6	$195.79	11.329%	$217.971	$217.97	$217.95	$218.00
Purchase #7	$10.38	4.572%	$10.8546	$10.85	$10.85	$10.90
7 purchase totals =	$601.52		$654.1977	$654.19	$654.10	$654.30