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	$73.25	13.316%	$83.004	$83.00	$83.00	$83.00
Purchase #2	$100.63	8.472%	$109.1554	$109.16	$109.15	$109.20
Purchase #3	$10.72	13.305%	$12.1463	$12.15	$12.15	$12.10
Purchase #4	$156.77	10.797%	$173.6965	$173.70	$173.70	$173.70
Purchase #5	$114.34	11.498%	$127.4868	$127.49	$127.50	$127.50
Purchase #6	$130.55	11.618%	$145.7173	$145.72	$145.70	$145.70
Purchase #7	$15.77	4.828%	$16.5314	$16.53	$16.55	$16.50
7 purchase totals =	$602.03		$667.7377	$667.75	$667.75	$667.70