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	$137.41	6.563%	$146.4282	$146.43	$146.45	$146.40
Purchase #2	$219.29	8.797%	$238.5809	$238.58	$238.60	$238.60
Purchase #3	$45.94	5.824%	$48.6155	$48.62	$48.60	$48.60
Purchase #4	$195.29	13.412%	$221.4823	$221.48	$221.50	$221.50
Purchase #5	$168.78	12.759%	$190.3146	$190.31	$190.30	$190.30
Purchase #6	$112.67	7.615%	$121.2498	$121.25	$121.25	$121.20
Purchase #7	$238.38	7.433%	$256.0988	$256.10	$256.10	$256.10
7 purchase totals =	$1,117.76		$1,222.7701	$1,222.77	$1,222.80	$1,222.70