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	$28.48	11.864%	$31.8589	$31.86	$31.85	$31.90
Purchase #2	$216.57	10.806%	$239.9726	$239.97	$239.95	$240.00
Purchase #3	$132.72	7.583%	$142.7842	$142.78	$142.80	$142.80
Purchase #4	$165.79	4.848%	$173.8275	$173.83	$173.85	$173.80
Purchase #5	$33.61	11.283%	$37.4022	$37.40	$37.40	$37.40
Purchase #6	$103.96	7.411%	$111.6645	$111.66	$111.65	$111.70
Purchase #7	$186.93	13.194%	$211.5935	$211.59	$211.60	$211.60
7 purchase totals =	$868.06		$949.1034	$949.09	$949.10	$949.20