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	$133.60	4.665%	$139.8324	$139.83	$139.85	$139.80
Purchase #2	$212.49	13.375%	$240.9105	$240.91	$240.90	$240.90
Purchase #3	$97.94	13.793%	$111.4489	$111.45	$111.45	$111.40
Purchase #4	$43.81	5.413%	$46.1814	$46.18	$46.20	$46.20
Purchase #5	$17.51	5.174%	$18.416	$18.42	$18.40	$18.40
Purchase #6	$217.94	10.542%	$240.9152	$240.92	$240.90	$240.90
Purchase #7	$165.61	11.370%	$184.4399	$184.44	$184.45	$184.40
7 purchase totals =	$888.90		$982.1443	$982.15	$982.15	$982.00