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	$24.45	8.482%	$26.5238	$26.52	$26.50	$26.50
Purchase #2	$129.81	7.510%	$139.5587	$139.56	$139.55	$139.60
Purchase #3	$156.30	6.834%	$166.9815	$166.98	$167.00	$167.00
Purchase #4	$33.62	5.243%	$35.3827	$35.38	$35.40	$35.40
Purchase #5	$145.52	7.271%	$156.1008	$156.10	$156.10	$156.10
Purchase #6	$12.47	7.510%	$13.4065	$13.41	$13.40	$13.40
Purchase #7	$147.86	7.222%	$158.5384	$158.54	$158.55	$158.50
7 purchase totals =	$650.03		$696.4924	$696.49	$696.50	$696.50