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	$231.82	4.214%	$241.5889	$241.59	$241.60	$241.60
Purchase #2	$90.97	9.554%	$99.6613	$99.66	$99.65	$99.70
Purchase #3	$68.25	3.188%	$70.4258	$70.43	$70.45	$70.40
Purchase #4	$17.70	8.257%	$19.1615	$19.16	$19.15	$19.20
Purchase #5	$103.66	5.628%	$109.494	$109.49	$109.50	$109.50
Purchase #6	$104.85	12.596%	$118.0569	$118.06	$118.05	$118.10
Purchase #7	$127.45	5.438%	$134.3807	$134.38	$134.40	$134.40
7 purchase totals =	$744.70		$792.7691	$792.77	$792.80	$792.90