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	$100.91	10.416%	$111.4208	$111.42	$111.40	$111.40
Purchase #2	$18.55	7.687%	$19.9759	$19.98	$20.00	$20.00
Purchase #3	$36.37	5.142%	$38.2401	$38.24	$38.25	$38.20
Purchase #4	$137.44	6.846%	$146.8491	$146.85	$146.85	$146.80
Purchase #5	$153.62	12.620%	$173.0068	$173.01	$173.00	$173.00
Purchase #6	$53.35	6.703%	$56.9261	$56.93	$56.95	$56.90
Purchase #7	$17.72	13.790%	$20.1636	$20.16	$20.15	$20.20
7 purchase totals =	$517.96		$566.5824	$566.59	$566.60	$566.50