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	$54.42	8.204%	$58.8846	$58.88	$58.90	$58.90
Purchase #2	$173.72	8.470%	$188.4341	$188.43	$188.45	$188.40
Purchase #3	$73.93	11.160%	$82.1806	$82.18	$82.20	$82.20
Purchase #4	$56.40	10.599%	$62.3778	$62.38	$62.40	$62.40
Purchase #5	$111.90	9.299%	$122.3056	$122.31	$122.30	$122.30
Purchase #6	$75.43	12.785%	$85.0737	$85.07	$85.05	$85.10
Purchase #7	$87.40	13.330%	$99.0504	$99.05	$99.05	$99.10
7 purchase totals =	$633.20		$698.3068	$698.30	$698.35	$698.40