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	$58.81	12.218%	$65.9954	$66.00	$66.00	$66.00
Purchase #2	$128.92	7.732%	$138.8881	$138.89	$138.90	$138.90
Purchase #3	$223.93	6.688%	$238.9064	$238.91	$238.90	$238.90
Purchase #4	$144.40	13.873%	$164.4326	$164.43	$164.45	$164.40
Purchase #5	$105.31	10.278%	$116.1338	$116.13	$116.15	$116.10
Purchase #6	$29.66	12.128%	$33.2572	$33.26	$33.25	$33.30
Purchase #7	$45.56	6.825%	$48.6695	$48.67	$48.65	$48.70
7 purchase totals =	$736.59		$806.2830	$806.29	$806.30	$806.30