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	$54.64	4.469%	$57.0819	$57.08	$57.10	$57.10
Purchase #2	$104.66	7.415%	$112.4205	$112.42	$112.40	$112.40
Purchase #3	$52.60	12.805%	$59.3354	$59.34	$59.35	$59.30
Purchase #4	$89.97	3.694%	$93.2935	$93.29	$93.30	$93.30
Purchase #5	$153.78	12.104%	$172.3935	$172.39	$172.40	$172.40
Purchase #6	$212.75	8.147%	$230.0827	$230.08	$230.10	$230.10
Purchase #7	$85.44	6.306%	$90.8278	$90.83	$90.85	$90.80
7 purchase totals =	$753.84		$815.4353	$815.43	$815.50	$815.40