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	$104.43	6.743%	$111.4717	$111.47	$111.45	$111.50
Purchase #2	$81.75	10.670%	$90.4727	$90.47	$90.45	$90.50
Purchase #3	$38.86	8.380%	$42.1165	$42.12	$42.10	$42.10
Purchase #4	$94.61	8.563%	$102.7115	$102.71	$102.70	$102.70
Purchase #5	$17.62	10.744%	$19.5131	$19.51	$19.50	$19.50
Purchase #6	$217.50	4.820%	$227.9835	$227.98	$228.00	$228.00
Purchase #7	$84.61	7.680%	$91.108	$91.11	$91.10	$91.10
7 purchase totals =	$639.38		$685.3770	$685.37	$685.30	$685.40