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	$49.70	3.577%	$51.4778	$51.48	$51.50	$51.50
Purchase #2	$50.45	10.614%	$55.8048	$55.80	$55.80	$55.80
Purchase #3	$40.71	4.443%	$42.5187	$42.52	$42.50	$42.50
Purchase #4	$78.67	3.675%	$81.5611	$81.56	$81.55	$81.60
Purchase #5	$42.44	13.677%	$48.2445	$48.24	$48.25	$48.20
Purchase #6	$133.78	9.634%	$146.6684	$146.67	$146.65	$146.70
Purchase #7	$132.82	8.723%	$144.4059	$144.41	$144.40	$144.40
7 purchase totals =	$528.57		$570.6812	$570.68	$570.65	$570.70