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	$46.90	8.461%	$50.8682	$50.87	$50.85	$50.90
Purchase #2	$53.31	11.520%	$59.4513	$59.45	$59.45	$59.50
Purchase #3	$46.27	4.841%	$48.5099	$48.51	$48.50	$48.50
Purchase #4	$88.76	4.557%	$92.8048	$92.80	$92.80	$92.80
Purchase #5	$250.40	12.726%	$282.2659	$282.27	$282.25	$282.30
Purchase #6	$15.83	7.846%	$17.072	$17.07	$17.05	$17.10
Purchase #7	$21.45	6.319%	$22.8054	$22.81	$22.80	$22.80
7 purchase totals =	$522.92		$573.7775	$573.78	$573.70	$573.90