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	$31.88	12.482%	$35.8593	$35.86	$35.85	$35.90
Purchase #2	$230.45	6.277%	$244.9153	$244.92	$244.90	$244.90
Purchase #3	$129.45	5.699%	$136.8274	$136.83	$136.85	$136.80
Purchase #4	$26.90	4.422%	$28.0895	$28.09	$28.10	$28.10
Purchase #5	$19.25	6.153%	$20.4345	$20.43	$20.45	$20.40
Purchase #6	$122.42	4.242%	$127.6131	$127.61	$127.60	$127.60
Purchase #7	$234.47	6.217%	$249.047	$249.05	$249.05	$249.00
7 purchase totals =	$794.82		$842.7861	$842.79	$842.80	$842.70