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	$105.25	5.622%	$111.1672	$111.17	$111.15	$111.20
Purchase #2	$175.47	4.123%	$182.7046	$182.70	$182.70	$182.70
Purchase #3	$132.83	10.370%	$146.6045	$146.60	$146.60	$146.60
Purchase #4	$95.27	6.640%	$101.5959	$101.60	$101.60	$101.60
Purchase #5	$165.87	13.490%	$188.2459	$188.25	$188.25	$188.20
Purchase #6	$40.87	10.131%	$45.0105	$45.01	$45.00	$45.00
Purchase #7	$105.99	8.620%	$115.1263	$115.13	$115.15	$115.10
7 purchase totals =	$821.55		$890.4549	$890.46	$890.45	$890.40