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	$107.37	11.851%	$120.0944	$120.09	$120.10	$120.10
Purchase #2	$115.74	10.405%	$127.7827	$127.78	$127.80	$127.80
Purchase #3	$24.39	4.801%	$25.561	$25.56	$25.55	$25.60
Purchase #4	$172.98	13.550%	$196.4188	$196.42	$196.40	$196.40
Purchase #5	$11.94	4.796%	$12.5126	$12.51	$12.50	$12.50
Purchase #6	$32.60	7.545%	$35.0597	$35.06	$35.05	$35.10
Purchase #7	$74.92	13.772%	$85.238	$85.24	$85.25	$85.20
7 purchase totals =	$539.94		$602.6672	$602.66	$602.65	$602.70