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	$71.94	12.177%	$80.7001	$80.70	$80.70	$80.70
Purchase #2	$31.92	5.761%	$33.7589	$33.76	$33.75	$33.80
Purchase #3	$151.46	10.145%	$166.8256	$166.83	$166.85	$166.80
Purchase #4	$115.39	6.848%	$123.2919	$123.29	$123.30	$123.30
Purchase #5	$9.50	6.566%	$10.1238	$10.12	$10.10	$10.10
Purchase #6	$93.52	11.252%	$104.0429	$104.04	$104.05	$104.00
Purchase #7	$167.52	3.662%	$173.6546	$173.65	$173.65	$173.70
7 purchase totals =	$641.25		$692.3978	$692.39	$692.40	$692.40