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	$58.35	12.620%	$65.7138	$65.71	$65.70	$65.70
Purchase #2	$151.52	12.404%	$170.3145	$170.31	$170.30	$170.30
Purchase #3	$156.82	10.625%	$173.4821	$173.48	$173.50	$173.50
Purchase #4	$94.42	13.612%	$107.2725	$107.27	$107.25	$107.30
Purchase #5	$125.38	4.572%	$131.1124	$131.11	$131.10	$131.10
Purchase #6	$57.45	6.175%	$60.9975	$61.00	$61.00	$61.00
Purchase #7	$159.53	8.385%	$172.9066	$172.91	$172.90	$172.90
7 purchase totals =	$803.47		$881.7994	$881.79	$881.75	$881.80