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	$18.39	6.784%	$19.6376	$19.64	$19.65	$19.60
Purchase #2	$93.32	11.286%	$103.8521	$103.85	$103.85	$103.90
Purchase #3	$170.45	5.361%	$179.5878	$179.59	$179.60	$179.60
Purchase #4	$230.29	13.148%	$260.5685	$260.57	$260.55	$260.60
Purchase #5	$112.77	4.745%	$118.1209	$118.12	$118.10	$118.10
Purchase #6	$136.45	7.400%	$146.5473	$146.55	$146.55	$146.50
Purchase #7	$134.74	11.735%	$150.5517	$150.55	$150.55	$150.60
7 purchase totals =	$896.41		$978.8659	$978.87	$978.85	$978.90