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	$49.90	5.418%	$52.6036	$52.60	$52.60	$52.60
Purchase #2	$54.49	13.258%	$61.7143	$61.71	$61.70	$61.70
Purchase #3	$74.46	12.169%	$83.521	$83.52	$83.50	$83.50
Purchase #4	$131.75	8.772%	$143.3071	$143.31	$143.30	$143.30
Purchase #5	$45.70	6.497%	$48.6691	$48.67	$48.65	$48.70
Purchase #6	$53.94	13.464%	$61.2025	$61.20	$61.20	$61.20
Purchase #7	$90.50	3.354%	$93.5354	$93.54	$93.55	$93.50
7 purchase totals =	$500.74		$544.5530	$544.55	$544.50	$544.50