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	$242.55	12.108%	$271.918	$271.92	$271.90	$271.90
Purchase #2	$91.64	9.510%	$100.355	$100.36	$100.35	$100.40
Purchase #3	$51.28	10.218%	$56.5198	$56.52	$56.50	$56.50
Purchase #4	$64.51	4.657%	$67.5142	$67.51	$67.50	$67.50
Purchase #5	$105.38	5.288%	$110.9525	$110.95	$110.95	$111.00
Purchase #6	$85.92	11.355%	$95.6762	$95.68	$95.70	$95.70
Purchase #7	$141.95	3.317%	$146.6585	$146.66	$146.65	$146.70
7 purchase totals =	$783.23		$849.5942	$849.60	$849.55	$849.70