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	$179.51	6.508%	$191.1925	$191.19	$191.20	$191.20
Purchase #2	$127.92	6.379%	$136.08	$136.08	$136.10	$136.10
Purchase #3	$82.66	9.387%	$90.4193	$90.42	$90.40	$90.40
Purchase #4	$37.86	3.204%	$39.073	$39.07	$39.05	$39.10
Purchase #5	$26.33	4.163%	$27.4261	$27.43	$27.45	$27.40
Purchase #6	$10.49	6.649%	$11.1875	$11.19	$11.20	$11.20
Purchase #7	$46.97	13.837%	$53.4692	$53.47	$53.45	$53.50
7 purchase totals =	$511.74		$548.8476	$548.85	$548.85	$548.90