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	$226.79	13.768%	$258.0144	$258.01	$258.00	$258.00
Purchase #2	$45.32	5.838%	$47.9658	$47.97	$47.95	$48.00
Purchase #3	$105.38	5.466%	$111.1401	$111.14	$111.15	$111.10
Purchase #4	$20.77	3.390%	$21.4741	$21.47	$21.45	$21.50
Purchase #5	$45.92	9.448%	$50.2585	$50.26	$50.25	$50.30
Purchase #6	$45.40	9.720%	$49.8129	$49.81	$49.80	$49.80
Purchase #7	$53.26	11.865%	$59.5793	$59.58	$59.60	$59.60
7 purchase totals =	$542.84		$598.2451	$598.24	$598.20	$598.30