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	$139.95	3.183%	$144.4046	$144.40	$144.40	$144.40
Purchase #2	$100.80	10.627%	$111.512	$111.51	$111.50	$111.50
Purchase #3	$9.89	4.610%	$10.3459	$10.35	$10.35	$10.30
Purchase #4	$95.52	11.295%	$106.309	$106.31	$106.30	$106.30
Purchase #5	$221.77	7.306%	$237.9725	$237.97	$237.95	$238.00
Purchase #6	$99.87	5.843%	$105.7054	$105.71	$105.70	$105.70
Purchase #7	$52.77	9.575%	$57.8227	$57.82	$57.80	$57.80
7 purchase totals =	$720.57		$774.0721	$774.07	$774.00	$774.00