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	$42.88	8.491%	$46.5209	$46.52	$46.50	$46.50
Purchase #2	$137.79	10.308%	$151.9934	$151.99	$152.00	$152.00
Purchase #3	$134.53	7.547%	$144.683	$144.68	$144.70	$144.70
Purchase #4	$35.97	5.691%	$38.0171	$38.02	$38.00	$38.00
Purchase #5	$56.92	4.308%	$59.3721	$59.37	$59.35	$59.40
Purchase #6	$138.91	10.644%	$153.6956	$153.70	$153.70	$153.70
Purchase #7	$42.77	9.466%	$46.8186	$46.82	$46.80	$46.80
7 purchase totals =	$589.77		$641.1007	$641.10	$641.05	$641.10