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	$112.75	9.182%	$123.1027	$123.10	$123.10	$123.10
Purchase #2	$56.92	12.218%	$63.8745	$63.87	$63.85	$63.90
Purchase #3	$145.38	4.493%	$151.9119	$151.91	$151.90	$151.90
Purchase #4	$43.95	10.229%	$48.4456	$48.45	$48.45	$48.40
Purchase #5	$246.47	13.872%	$280.6603	$280.66	$280.65	$280.70
Purchase #6	$22.75	11.108%	$25.2771	$25.28	$25.30	$25.30
Purchase #7	$119.57	5.643%	$126.3173	$126.32	$126.30	$126.30
7 purchase totals =	$747.79		$819.5894	$819.59	$819.55	$819.60