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	$46.86	5.494%	$49.4345	$49.43	$49.45	$49.40
Purchase #2	$132.77	9.414%	$145.269	$145.27	$145.25	$145.30
Purchase #3	$77.85	7.371%	$83.5883	$83.59	$83.60	$83.60
Purchase #4	$196.86	9.683%	$215.922	$215.92	$215.90	$215.90
Purchase #5	$183.69	8.244%	$198.8334	$198.83	$198.85	$198.80
Purchase #6	$39.43	6.285%	$41.9082	$41.91	$41.90	$41.90
Purchase #7	$158.83	4.485%	$165.9535	$165.95	$165.95	$166.00
7 purchase totals =	$836.29		$900.9089	$900.90	$900.90	$900.90