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	$141.37	5.130%	$148.6223	$148.62	$148.60	$148.60
Purchase #2	$137.68	13.603%	$156.4086	$156.41	$156.40	$156.40
Purchase #3	$206.44	6.255%	$219.3528	$219.35	$219.35	$219.40
Purchase #4	$48.38	8.432%	$52.4594	$52.46	$52.45	$52.50
Purchase #5	$171.51	10.788%	$190.0125	$190.01	$190.00	$190.00
Purchase #6	$37.59	10.803%	$41.6508	$41.65	$41.65	$41.70
Purchase #7	$173.48	9.551%	$190.0491	$190.05	$190.05	$190.00
7 purchase totals =	$916.45		$998.5555	$998.55	$998.50	$998.60