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	$92.89	7.832%	$100.1651	$100.17	$100.15	$100.20
Purchase #2	$18.31	12.684%	$20.6324	$20.63	$20.65	$20.60
Purchase #3	$67.49	7.223%	$72.3648	$72.36	$72.35	$72.40
Purchase #4	$52.82	3.414%	$54.6233	$54.62	$54.60	$54.60
Purchase #5	$13.84	13.353%	$15.6881	$15.69	$15.70	$15.70
Purchase #6	$179.60	13.607%	$204.0382	$204.04	$204.05	$204.00
Purchase #7	$107.88	6.703%	$115.1112	$115.11	$115.10	$115.10
7 purchase totals =	$532.83		$582.6231	$582.62	$582.60	$582.60