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	$11.35	8.107%	$12.2701	$12.27	$12.25	$12.30
Purchase #2	$45.91	11.523%	$51.2002	$51.20	$51.20	$51.20
Purchase #3	$181.87	12.415%	$204.4492	$204.45	$204.45	$204.40
Purchase #4	$196.65	10.105%	$216.5215	$216.52	$216.50	$216.50
Purchase #5	$128.92	7.286%	$138.3131	$138.31	$138.30	$138.30
Purchase #6	$152.90	13.513%	$173.5614	$173.56	$173.55	$173.60
Purchase #7	$166.98	9.379%	$182.6411	$182.64	$182.65	$182.60
7 purchase totals =	$884.58		$978.9566	$978.95	$978.90	$978.90