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	$104.58	6.531%	$111.4101	$111.41	$111.40	$111.40
Purchase #2	$108.96	4.697%	$114.0779	$114.08	$114.10	$114.10
Purchase #3	$49.51	4.598%	$51.7865	$51.79	$51.80	$51.80
Purchase #4	$181.90	13.526%	$206.5038	$206.50	$206.50	$206.50
Purchase #5	$53.28	10.312%	$58.7742	$58.77	$58.75	$58.80
Purchase #6	$62.37	4.299%	$65.0513	$65.05	$65.05	$65.10
Purchase #7	$30.38	11.366%	$33.833	$33.83	$33.85	$33.80
7 purchase totals =	$590.98		$641.4368	$641.43	$641.45	$641.50