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	$11.29	11.639%	$12.604	$12.60	$12.60	$12.60
Purchase #2	$96.82	10.341%	$106.8322	$106.83	$106.85	$106.80
Purchase #3	$71.74	9.678%	$78.683	$78.68	$78.70	$78.70
Purchase #4	$105.26	13.259%	$119.2164	$119.22	$119.20	$119.20
Purchase #5	$236.54	8.154%	$255.8275	$255.83	$255.85	$255.80
Purchase #6	$75.25	11.534%	$83.9293	$83.93	$83.95	$83.90
Purchase #7	$30.98	13.607%	$35.1954	$35.20	$35.20	$35.20
7 purchase totals =	$627.88		$692.2878	$692.29	$692.35	$692.20