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	$138.88	12.636%	$156.4289	$156.43	$156.45	$156.40
Purchase #2	$246.27	11.572%	$274.7684	$274.77	$274.75	$274.80
Purchase #3	$224.26	4.382%	$234.0871	$234.09	$234.10	$234.10
Purchase #4	$52.99	3.576%	$54.8849	$54.88	$54.90	$54.90
Purchase #5	$139.79	13.301%	$158.3835	$158.38	$158.40	$158.40
Purchase #6	$107.52	3.430%	$111.2079	$111.21	$111.20	$111.20
Purchase #7	$62.52	3.827%	$64.9126	$64.91	$64.90	$64.90
7 purchase totals =	$972.23		$1,054.6733	$1,054.67	$1,054.70	$1,054.70