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	$132.78	13.246%	$150.368	$150.37	$150.35	$150.40
Purchase #2	$176.65	5.339%	$186.0813	$186.08	$186.10	$186.10
Purchase #3	$96.56	11.302%	$107.4732	$107.47	$107.45	$107.50
Purchase #4	$86.89	10.679%	$96.169	$96.17	$96.15	$96.20
Purchase #5	$89.52	10.637%	$99.0422	$99.04	$99.05	$99.00
Purchase #6	$76.91	8.565%	$83.4973	$83.50	$83.50	$83.50
Purchase #7	$241.92	6.757%	$258.2665	$258.27	$258.25	$258.30
7 purchase totals =	$901.23		$980.8975	$980.90	$980.85	$981.00