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	$36.46	10.798%	$40.397	$40.40	$40.40	$40.40
Purchase #2	$59.84	13.466%	$67.8981	$67.90	$67.90	$67.90
Purchase #3	$225.48	11.757%	$251.9897	$251.99	$252.00	$252.00
Purchase #4	$82.82	10.793%	$91.7588	$91.76	$91.75	$91.80
Purchase #5	$47.85	9.671%	$52.4776	$52.48	$52.50	$52.50
Purchase #6	$56.52	6.657%	$60.2825	$60.28	$60.30	$60.30
Purchase #7	$49.85	7.839%	$53.7577	$53.76	$53.75	$53.80
7 purchase totals =	$558.82		$618.5614	$618.57	$618.60	$618.70