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	$62.85	6.323%	$66.824	$66.82	$66.80	$66.80
Purchase #2	$134.97	11.864%	$150.9828	$150.98	$151.00	$151.00
Purchase #3	$152.86	11.145%	$169.8962	$169.90	$169.90	$169.90
Purchase #4	$58.58	12.104%	$65.6705	$65.67	$65.65	$65.70
Purchase #5	$167.60	3.137%	$172.8576	$172.86	$172.85	$172.90
Purchase #6	$29.45	8.252%	$31.8802	$31.88	$31.90	$31.90
Purchase #7	$24.98	12.308%	$28.0545	$28.05	$28.05	$28.10
7 purchase totals =	$631.29		$686.1658	$686.16	$686.15	$686.30