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	$81.76	13.598%	$92.8777	$92.88	$92.90	$92.90
Purchase #2	$132.47	12.699%	$149.2924	$149.29	$149.30	$149.30
Purchase #3	$139.36	10.619%	$154.1586	$154.16	$154.15	$154.20
Purchase #4	$118.43	7.682%	$127.5278	$127.53	$127.55	$127.50
Purchase #5	$204.27	8.474%	$221.5798	$221.58	$221.60	$221.60
Purchase #6	$9.35	12.486%	$10.5174	$10.52	$10.50	$10.50
Purchase #7	$135.39	4.778%	$141.8589	$141.86	$141.85	$141.90
7 purchase totals =	$821.03		$897.8126	$897.82	$897.85	$897.90