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	$173.31	6.510%	$184.5925	$184.59	$184.60	$184.60
Purchase #2	$99.53	11.833%	$111.3074	$111.31	$111.30	$111.30
Purchase #3	$181.54	3.246%	$187.4328	$187.43	$187.45	$187.40
Purchase #4	$70.87	10.182%	$78.086	$78.09	$78.10	$78.10
Purchase #5	$141.93	8.304%	$153.7159	$153.72	$153.70	$153.70
Purchase #6	$47.89	9.387%	$52.3854	$52.39	$52.40	$52.40
Purchase #7	$196.41	4.673%	$205.5882	$205.59	$205.60	$205.60
7 purchase totals =	$911.48		$973.1082	$973.12	$973.15	$973.10