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	$40.25	10.688%	$44.5519	$44.55	$44.55	$44.60
Purchase #2	$209.97	10.419%	$231.8468	$231.85	$231.85	$231.80
Purchase #3	$139.43	13.745%	$158.5947	$158.59	$158.60	$158.60
Purchase #4	$191.54	13.536%	$217.4669	$217.47	$217.45	$217.50
Purchase #5	$122.37	4.152%	$127.4508	$127.45	$127.45	$127.50
Purchase #6	$87.47	10.465%	$96.6237	$96.62	$96.60	$96.60
Purchase #7	$37.40	11.359%	$41.6483	$41.65	$41.65	$41.60
7 purchase totals =	$828.43		$918.1831	$918.18	$918.15	$918.20