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	$138.59	5.336%	$145.9852	$145.99	$146.00	$146.00
Purchase #2	$101.85	12.466%	$114.5466	$114.55	$114.55	$114.50
Purchase #3	$142.68	3.862%	$148.1903	$148.19	$148.20	$148.20
Purchase #4	$38.29	11.504%	$42.6949	$42.69	$42.70	$42.70
Purchase #5	$77.89	5.803%	$82.41	$82.41	$82.40	$82.40
Purchase #6	$30.32	12.572%	$34.1318	$34.13	$34.15	$34.10
Purchase #7	$48.28	13.708%	$54.8982	$54.90	$54.90	$54.90
7 purchase totals =	$577.90		$622.8570	$622.86	$622.90	$622.80