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	$32.60	9.615%	$35.7345	$35.73	$35.75	$35.70
Purchase #2	$196.28	8.252%	$212.477	$212.48	$212.50	$212.50
Purchase #3	$138.78	12.762%	$156.4911	$156.49	$156.50	$156.50
Purchase #4	$72.58	8.542%	$78.7798	$78.78	$78.80	$78.80
Purchase #5	$118.81	7.611%	$127.8526	$127.85	$127.85	$127.90
Purchase #6	$11.40	11.784%	$12.7434	$12.74	$12.75	$12.70
Purchase #7	$24.70	6.492%	$26.3035	$26.30	$26.30	$26.30
7 purchase totals =	$595.15		$650.3819	$650.37	$650.45	$650.40