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	$56.80	9.645%	$62.2784	$62.28	$62.30	$62.30
Purchase #2	$68.87	8.592%	$74.7873	$74.79	$74.80	$74.80
Purchase #3	$179.34	3.228%	$185.1291	$185.13	$185.15	$185.10
Purchase #4	$173.65	13.228%	$196.6204	$196.62	$196.60	$196.60
Purchase #5	$153.37	12.418%	$172.4155	$172.42	$172.40	$172.40
Purchase #6	$12.81	8.108%	$13.8486	$13.85	$13.85	$13.80
Purchase #7	$74.77	7.469%	$80.3546	$80.35	$80.35	$80.40
7 purchase totals =	$719.61		$785.4339	$785.44	$785.45	$785.40