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	$159.92	11.822%	$178.8257	$178.83	$178.85	$178.80
Purchase #2	$169.96	5.178%	$178.7605	$178.76	$178.75	$178.80
Purchase #3	$230.51	4.619%	$241.1573	$241.16	$241.15	$241.20
Purchase #4	$55.73	6.763%	$59.499	$59.50	$59.50	$59.50
Purchase #5	$48.37	8.386%	$52.4263	$52.43	$52.45	$52.40
Purchase #6	$107.91	3.861%	$112.0764	$112.08	$112.10	$112.10
Purchase #7	$166.65	7.299%	$178.8138	$178.81	$178.80	$178.80
7 purchase totals =	$939.05		$1,001.5590	$1,001.57	$1,001.60	$1,001.60