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	$173.80	3.782%	$180.3731	$180.37	$180.35	$180.40
Purchase #2	$110.80	6.466%	$117.9643	$117.96	$117.95	$118.00
Purchase #3	$52.63	13.323%	$59.6419	$59.64	$59.65	$59.60
Purchase #4	$103.98	12.493%	$116.9702	$116.97	$116.95	$117.00
Purchase #5	$87.86	3.618%	$91.0388	$91.04	$91.05	$91.00
Purchase #6	$62.88	5.655%	$66.4359	$66.44	$66.45	$66.40
Purchase #7	$47.85	13.407%	$54.2652	$54.27	$54.25	$54.30
7 purchase totals =	$639.80		$686.6894	$686.69	$686.65	$686.70