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	$35.43	11.691%	$39.5721	$39.57	$39.55	$39.60
Purchase #2	$46.56	11.538%	$51.9321	$51.93	$51.95	$51.90
Purchase #3	$116.86	9.124%	$127.5223	$127.52	$127.50	$127.50
Purchase #4	$19.51	4.640%	$20.4153	$20.42	$20.40	$20.40
Purchase #5	$62.68	3.102%	$64.6243	$64.62	$64.60	$64.60
Purchase #6	$49.39	10.646%	$54.6481	$54.65	$54.65	$54.60
Purchase #7	$66.83	6.526%	$71.1913	$71.19	$71.20	$71.20
7 purchase totals =	$397.26		$429.9055	$429.90	$429.85	$429.80