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	$250.85	11.419%	$279.4946	$279.49	$279.50	$279.50
Purchase #2	$181.53	13.647%	$206.3034	$206.30	$206.30	$206.30
Purchase #3	$187.42	11.794%	$209.5243	$209.52	$209.50	$209.50
Purchase #4	$248.79	12.450%	$279.7644	$279.76	$279.75	$279.80
Purchase #5	$51.56	5.582%	$54.4381	$54.44	$54.45	$54.40
Purchase #6	$36.43	8.585%	$39.5575	$39.56	$39.55	$39.60
Purchase #7	$94.82	10.767%	$105.0293	$105.03	$105.05	$105.00
7 purchase totals =	$1,051.40		$1,174.1116	$1,174.10	$1,174.10	$1,174.10