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	$156.37	6.251%	$166.1447	$166.14	$166.15	$166.10
Purchase #2	$147.82	7.348%	$158.6818	$158.68	$158.70	$158.70
Purchase #3	$78.71	8.130%	$85.1091	$85.11	$85.10	$85.10
Purchase #4	$133.39	6.842%	$142.5165	$142.52	$142.50	$142.50
Purchase #5	$111.68	6.439%	$118.8711	$118.87	$118.85	$118.90
Purchase #6	$199.46	12.671%	$224.7336	$224.73	$224.75	$224.70
Purchase #7	$50.61	3.848%	$52.5575	$52.56	$52.55	$52.60
7 purchase totals =	$878.04		$948.6143	$948.61	$948.60	$948.60