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	$54.26	5.365%	$57.171	$57.17	$57.15	$57.20
Purchase #2	$106.30	9.724%	$116.6366	$116.64	$116.65	$116.60
Purchase #3	$62.39	5.105%	$65.575	$65.58	$65.60	$65.60
Purchase #4	$99.49	4.189%	$103.6576	$103.66	$103.65	$103.70
Purchase #5	$107.39	4.163%	$111.8606	$111.86	$111.85	$111.90
Purchase #6	$180.25	3.865%	$187.2167	$187.22	$187.20	$187.20
Purchase #7	$182.67	8.722%	$198.6025	$198.60	$198.60	$198.60
7 purchase totals =	$792.75		$840.7200	$840.73	$840.70	$840.80