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	$75.67	7.298%	$81.1924	$81.19	$81.20	$81.20
Purchase #2	$68.98	5.188%	$72.5587	$72.56	$72.55	$72.60
Purchase #3	$49.49	9.194%	$54.0401	$54.04	$54.05	$54.00
Purchase #4	$40.49	3.410%	$41.8707	$41.87	$41.85	$41.90
Purchase #5	$151.52	6.569%	$161.4733	$161.47	$161.45	$161.50
Purchase #6	$155.45	10.755%	$172.1686	$172.17	$172.15	$172.20
Purchase #7	$83.80	12.453%	$94.2356	$94.24	$94.25	$94.20
7 purchase totals =	$625.40		$677.5394	$677.54	$677.50	$677.60