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	$97.53	6.771%	$104.1338	$104.13	$104.15	$104.10
Purchase #2	$16.39	9.259%	$17.9076	$17.91	$17.90	$17.90
Purchase #3	$145.55	10.326%	$160.5795	$160.58	$160.60	$160.60
Purchase #4	$41.76	3.702%	$43.306	$43.31	$43.30	$43.30
Purchase #5	$80.28	3.181%	$82.8337	$82.83	$82.85	$82.80
Purchase #6	$141.82	10.487%	$156.6927	$156.69	$156.70	$156.70
Purchase #7	$10.60	8.395%	$11.4899	$11.49	$11.50	$11.50
7 purchase totals =	$533.93		$576.9432	$576.94	$577.00	$576.90