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	$204.84	6.662%	$218.4864	$218.49	$218.50	$218.50
Purchase #2	$101.36	9.691%	$111.1828	$111.18	$111.20	$111.20
Purchase #3	$233.70	5.722%	$247.0723	$247.07	$247.05	$247.10
Purchase #4	$47.45	8.630%	$51.5449	$51.54	$51.55	$51.50
Purchase #5	$183.39	4.596%	$191.8186	$191.82	$191.80	$191.80
Purchase #6	$59.66	9.816%	$65.5162	$65.52	$65.50	$65.50
Purchase #7	$249.87	3.420%	$258.4156	$258.42	$258.40	$258.40
7 purchase totals =	$1,080.27		$1,144.0368	$1,144.04	$1,144.00	$1,144.00