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	$250.94	8.764%	$272.9324	$272.93	$272.95	$272.90
Purchase #2	$83.75	7.453%	$89.9919	$89.99	$90.00	$90.00
Purchase #3	$101.46	9.468%	$111.0662	$111.07	$111.05	$111.10
Purchase #4	$131.85	10.664%	$145.9105	$145.91	$145.90	$145.90
Purchase #5	$208.95	10.171%	$230.2023	$230.20	$230.20	$230.20
Purchase #6	$191.90	11.593%	$214.147	$214.15	$214.15	$214.10
Purchase #7	$75.55	4.136%	$78.6747	$78.67	$78.65	$78.70
7 purchase totals =	$1,044.40		$1,142.9250	$1,142.92	$1,142.90	$1,142.90