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	$220.33	11.462%	$245.5842	$245.58	$245.60	$245.60
Purchase #2	$132.45	8.186%	$143.2924	$143.29	$143.30	$143.30
Purchase #3	$49.45	7.534%	$53.1756	$53.18	$53.20	$53.20
Purchase #4	$230.50	5.792%	$243.8506	$243.85	$243.85	$243.90
Purchase #5	$45.90	4.457%	$47.9458	$47.95	$47.95	$47.90
Purchase #6	$42.47	13.547%	$48.2234	$48.22	$48.20	$48.20
Purchase #7	$133.43	6.758%	$142.4472	$142.45	$142.45	$142.40
7 purchase totals =	$854.53		$924.5192	$924.52	$924.55	$924.50