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	$121.97	4.259%	$127.1647	$127.16	$127.15	$127.20
Purchase #2	$91.68	11.733%	$102.4368	$102.44	$102.45	$102.40
Purchase #3	$34.46	13.191%	$39.0056	$39.01	$39.00	$39.00
Purchase #4	$99.93	8.217%	$108.1412	$108.14	$108.15	$108.10
Purchase #5	$213.84	4.152%	$222.7186	$222.72	$222.70	$222.70
Purchase #6	$29.65	6.335%	$31.5283	$31.53	$31.55	$31.50
Purchase #7	$18.75	3.517%	$19.4094	$19.41	$19.40	$19.40
7 purchase totals =	$610.28		$650.4046	$650.41	$650.40	$650.30