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	$151.26	9.784%	$166.0593	$166.06	$166.05	$166.10
Purchase #2	$43.47	5.467%	$45.8465	$45.85	$45.85	$45.80
Purchase #3	$72.82	4.672%	$76.2222	$76.22	$76.20	$76.20
Purchase #4	$97.75	3.307%	$100.9826	$100.98	$101.00	$101.00
Purchase #5	$66.65	8.425%	$72.2653	$72.27	$72.25	$72.30
Purchase #6	$30.95	10.281%	$34.132	$34.13	$34.15	$34.10
Purchase #7	$23.72	13.215%	$26.8546	$26.85	$26.85	$26.90
7 purchase totals =	$486.62		$522.3625	$522.36	$522.35	$522.40