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	$37.46	5.608%	$39.5608	$39.56	$39.55	$39.60
Purchase #2	$203.53	5.340%	$214.3985	$214.40	$214.40	$214.40
Purchase #3	$104.28	13.717%	$118.5841	$118.58	$118.60	$118.60
Purchase #4	$224.56	7.174%	$240.6699	$240.67	$240.65	$240.70
Purchase #5	$122.64	5.262%	$129.0933	$129.09	$129.10	$129.10
Purchase #6	$158.39	5.190%	$166.6104	$166.61	$166.60	$166.60
Purchase #7	$177.56	10.706%	$196.5696	$196.57	$196.55	$196.60
7 purchase totals =	$1,028.42		$1,105.4866	$1,105.48	$1,105.45	$1,105.60