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	$55.64	4.191%	$57.9719	$57.97	$57.95	$58.00
Purchase #2	$100.96	4.844%	$105.8505	$105.85	$105.85	$105.90
Purchase #3	$185.73	13.111%	$210.0811	$210.08	$210.10	$210.10
Purchase #4	$49.33	7.240%	$52.9015	$52.90	$52.90	$52.90
Purchase #5	$136.92	9.387%	$149.7727	$149.77	$149.75	$149.80
Purchase #6	$9.77	10.724%	$10.8177	$10.82	$10.80	$10.80
Purchase #7	$230.81	12.117%	$258.7772	$258.78	$258.80	$258.80
7 purchase totals =	$769.16		$846.1726	$846.17	$846.15	$846.30