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	$230.50	12.569%	$259.4715	$259.47	$259.45	$259.50
Purchase #2	$181.72	10.149%	$200.1628	$200.16	$200.15	$200.20
Purchase #3	$188.52	6.339%	$200.4703	$200.47	$200.45	$200.50
Purchase #4	$158.76	8.682%	$172.5435	$172.54	$172.55	$172.50
Purchase #5	$18.61	4.349%	$19.4193	$19.42	$19.40	$19.40
Purchase #6	$25.88	6.829%	$27.6473	$27.65	$27.65	$27.60
Purchase #7	$236.81	5.471%	$249.7659	$249.77	$249.75	$249.80
7 purchase totals =	$1,040.80		$1,129.4806	$1,129.48	$1,129.40	$1,129.50