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	$54.29	11.354%	$60.4541	$60.45	$60.45	$60.50
Purchase #2	$70.56	12.873%	$79.6432	$79.64	$79.65	$79.60
Purchase #3	$39.42	8.245%	$42.6702	$42.67	$42.65	$42.70
Purchase #4	$231.57	11.319%	$257.7814	$257.78	$257.80	$257.80
Purchase #5	$227.45	4.846%	$238.4722	$238.47	$238.45	$238.50
Purchase #6	$53.50	5.795%	$56.6003	$56.60	$56.60	$56.60
Purchase #7	$104.81	4.501%	$109.5275	$109.53	$109.55	$109.50
7 purchase totals =	$781.60		$845.1489	$845.14	$845.15	$845.20