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	$44.46	13.155%	$50.3087	$50.31	$50.30	$50.30
Purchase #2	$97.33	11.340%	$108.3672	$108.37	$108.35	$108.40
Purchase #3	$163.66	11.854%	$183.0603	$183.06	$183.05	$183.10
Purchase #4	$178.83	11.710%	$199.771	$199.77	$199.75	$199.80
Purchase #5	$107.87	4.288%	$112.4955	$112.50	$112.50	$112.50
Purchase #6	$96.72	9.301%	$105.7159	$105.72	$105.70	$105.70
Purchase #7	$211.77	5.242%	$222.871	$222.87	$222.85	$222.90
7 purchase totals =	$900.64		$982.5896	$982.60	$982.50	$982.70