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	$146.28	13.285%	$165.7133	$165.71	$165.70	$165.70
Purchase #2	$22.73	10.571%	$25.1328	$25.13	$25.15	$25.10
Purchase #3	$152.67	9.659%	$167.4164	$167.42	$167.40	$167.40
Purchase #4	$214.89	8.702%	$233.5897	$233.59	$233.60	$233.60
Purchase #5	$52.85	9.243%	$57.7349	$57.73	$57.75	$57.70
Purchase #6	$33.55	5.491%	$35.3922	$35.39	$35.40	$35.40
Purchase #7	$93.43	11.837%	$104.4893	$104.49	$104.50	$104.50
7 purchase totals =	$716.40		$789.4686	$789.46	$789.50	$789.40