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	$106.69	11.144%	$118.5795	$118.58	$118.60	$118.60
Purchase #2	$182.55	7.457%	$196.1628	$196.16	$196.15	$196.20
Purchase #3	$153.46	4.137%	$159.8086	$159.81	$159.80	$159.80
Purchase #4	$103.63	12.563%	$116.649	$116.65	$116.65	$116.60
Purchase #5	$119.65	7.337%	$128.4287	$128.43	$128.45	$128.40
Purchase #6	$91.85	12.822%	$103.627	$103.63	$103.65	$103.60
Purchase #7	$138.93	10.873%	$154.0359	$154.04	$154.05	$154.00
7 purchase totals =	$896.76		$977.2915	$977.30	$977.35	$977.20