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	$112.90	6.631%	$120.3864	$120.39	$120.40	$120.40
Purchase #2	$111.40	5.367%	$117.3788	$117.38	$117.40	$117.40
Purchase #3	$17.97	6.723%	$19.1781	$19.18	$19.20	$19.20
Purchase #4	$103.30	4.548%	$107.9981	$108.00	$108.00	$108.00
Purchase #5	$150.29	11.323%	$167.3073	$167.31	$167.30	$167.30
Purchase #6	$28.25	12.292%	$31.7225	$31.72	$31.70	$31.70
Purchase #7	$101.71	9.761%	$111.6379	$111.64	$111.65	$111.60
7 purchase totals =	$625.82		$675.6091	$675.62	$675.65	$675.60