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	$202.71	10.487%	$223.9682	$223.97	$223.95	$224.00
Purchase #2	$85.97	4.487%	$89.8275	$89.83	$89.85	$89.80
Purchase #3	$79.62	12.323%	$89.4316	$89.43	$89.45	$89.40
Purchase #4	$171.91	6.721%	$183.4641	$183.46	$183.45	$183.50
Purchase #5	$45.46	6.185%	$48.2717	$48.27	$48.25	$48.30
Purchase #6	$11.71	8.462%	$12.7009	$12.70	$12.70	$12.70
Purchase #7	$91.43	10.262%	$100.8125	$100.81	$100.80	$100.80
7 purchase totals =	$688.81		$748.4765	$748.47	$748.45	$748.50