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	$30.34	13.550%	$34.4511	$34.45	$34.45	$34.50
Purchase #2	$181.59	10.209%	$200.1285	$200.13	$200.15	$200.10
Purchase #3	$206.54	5.343%	$217.5754	$217.58	$217.60	$217.60
Purchase #4	$108.72	4.475%	$113.5852	$113.59	$113.60	$113.60
Purchase #5	$167.59	10.582%	$185.3244	$185.32	$185.30	$185.30
Purchase #6	$68.64	8.746%	$74.6433	$74.64	$74.65	$74.60
Purchase #7	$144.89	6.121%	$153.7587	$153.76	$153.75	$153.80
7 purchase totals =	$908.31		$979.4666	$979.47	$979.50	$979.50