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	$17.76	13.466%	$20.1516	$20.15	$20.15	$20.20
Purchase #2	$141.91	12.205%	$159.2301	$159.23	$159.25	$159.20
Purchase #3	$46.64	10.255%	$51.4229	$51.42	$51.40	$51.40
Purchase #4	$54.54	9.107%	$59.507	$59.51	$59.50	$59.50
Purchase #5	$241.77	3.202%	$249.5115	$249.51	$249.50	$249.50
Purchase #6	$41.49	3.266%	$42.8451	$42.85	$42.85	$42.80
Purchase #7	$231.74	3.408%	$239.6377	$239.64	$239.65	$239.60
7 purchase totals =	$775.85		$822.3059	$822.31	$822.30	$822.20