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	$168.31	6.589%	$179.3999	$179.40	$179.40	$179.40
Purchase #2	$130.38	10.795%	$144.4545	$144.45	$144.45	$144.50
Purchase #3	$148.34	4.721%	$155.3431	$155.34	$155.35	$155.30
Purchase #4	$187.62	5.670%	$198.2581	$198.26	$198.25	$198.30
Purchase #5	$109.41	4.721%	$114.5752	$114.58	$114.60	$114.60
Purchase #6	$48.46	13.130%	$54.8228	$54.82	$54.80	$54.80
Purchase #7	$134.52	6.343%	$143.0526	$143.05	$143.05	$143.10
7 purchase totals =	$927.04		$989.9062	$989.90	$989.90	$990.00