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	$89.36	12.586%	$100.6068	$100.61	$100.60	$100.60
Purchase #2	$34.93	7.301%	$37.4802	$37.48	$37.50	$37.50
Purchase #3	$26.82	6.310%	$28.5123	$28.51	$28.50	$28.50
Purchase #4	$40.53	6.429%	$43.1357	$43.14	$43.15	$43.10
Purchase #5	$214.68	9.509%	$235.0939	$235.09	$235.10	$235.10
Purchase #6	$10.98	9.385%	$12.0105	$12.01	$12.00	$12.00
Purchase #7	$176.42	3.802%	$183.1275	$183.13	$183.15	$183.10
7 purchase totals =	$593.72		$639.9669	$639.97	$640.00	$639.90