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	$37.49	10.485%	$41.4208	$41.42	$41.40	$41.40
Purchase #2	$111.98	11.672%	$125.0503	$125.05	$125.05	$125.10
Purchase #3	$54.98	7.615%	$59.1667	$59.17	$59.15	$59.20
Purchase #4	$115.76	6.756%	$123.5807	$123.58	$123.60	$123.60
Purchase #5	$126.58	12.341%	$142.2012	$142.20	$142.20	$142.20
Purchase #6	$59.85	5.666%	$63.2411	$63.24	$63.25	$63.20
Purchase #7	$100.37	7.242%	$107.6388	$107.64	$107.65	$107.60
7 purchase totals =	$607.01		$662.2996	$662.30	$662.30	$662.30