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	$59.42	11.186%	$66.0667	$66.07	$66.05	$66.10
Purchase #2	$233.92	9.439%	$255.9997	$256.00	$256.00	$256.00
Purchase #3	$233.94	10.466%	$258.4242	$258.42	$258.40	$258.40
Purchase #4	$98.25	7.145%	$105.27	$105.27	$105.25	$105.30
Purchase #5	$191.78	4.543%	$200.4926	$200.49	$200.50	$200.50
Purchase #6	$245.76	9.785%	$269.8076	$269.81	$269.80	$269.80
Purchase #7	$83.38	10.425%	$92.0724	$92.07	$92.05	$92.10
7 purchase totals =	$1,146.45		$1,248.1332	$1,248.13	$1,248.05	$1,248.20