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	$243.61	13.125%	$275.5838	$275.58	$275.60	$275.60
Purchase #2	$120.35	8.602%	$130.7025	$130.70	$130.70	$130.70
Purchase #3	$140.88	11.332%	$156.8445	$156.84	$156.85	$156.80
Purchase #4	$192.48	4.113%	$200.3967	$200.40	$200.40	$200.40
Purchase #5	$49.48	10.145%	$54.4997	$54.50	$54.50	$54.50
Purchase #6	$142.59	6.664%	$152.0922	$152.09	$152.10	$152.10
Purchase #7	$117.42	13.830%	$133.6592	$133.66	$133.65	$133.70
7 purchase totals =	$1,006.81		$1,103.7786	$1,103.77	$1,103.80	$1,103.80