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	$181.88	13.659%	$206.723	$206.72	$206.70	$206.70
Purchase #2	$100.71	11.665%	$112.4578	$112.46	$112.45	$112.50
Purchase #3	$205.71	9.180%	$224.5942	$224.59	$224.60	$224.60
Purchase #4	$50.48	8.206%	$54.6224	$54.62	$54.60	$54.60
Purchase #5	$5.74	10.126%	$6.3212	$6.32	$6.30	$6.30
Purchase #6	$118.82	7.135%	$127.2978	$127.30	$127.30	$127.30
Purchase #7	$142.83	8.615%	$155.1348	$155.13	$155.15	$155.10
7 purchase totals =	$806.17		$887.1512	$887.14	$887.10	$887.10