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	$47.73	13.121%	$53.9927	$53.99	$54.00	$54.00
Purchase #2	$104.87	6.330%	$111.5083	$111.51	$111.50	$111.50
Purchase #3	$100.78	11.559%	$112.4292	$112.43	$112.45	$112.40
Purchase #4	$144.75	10.715%	$160.26	$160.26	$160.25	$160.30
Purchase #5	$55.64	8.582%	$60.415	$60.42	$60.40	$60.40
Purchase #6	$13.66	3.581%	$14.1492	$14.15	$14.15	$14.10
Purchase #7	$235.70	5.808%	$249.3895	$249.39	$249.40	$249.40
7 purchase totals =	$703.13		$762.1439	$762.15	$762.15	$762.10