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	$11.78	8.829%	$12.8201	$12.82	$12.80	$12.80
Purchase #2	$137.83	4.683%	$144.2846	$144.28	$144.30	$144.30
Purchase #3	$48.51	5.546%	$51.2004	$51.20	$51.20	$51.20
Purchase #4	$57.38	5.657%	$60.626	$60.63	$60.65	$60.60
Purchase #5	$108.62	3.832%	$112.7823	$112.78	$112.80	$112.80
Purchase #6	$174.50	6.289%	$185.4743	$185.47	$185.45	$185.50
Purchase #7	$78.98	13.107%	$89.3319	$89.33	$89.35	$89.30
7 purchase totals =	$617.60		$656.5196	$656.51	$656.55	$656.50