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	$164.34	7.499%	$176.6639	$176.66	$176.65	$176.70
Purchase #2	$45.63	3.391%	$47.1773	$47.18	$47.20	$47.20
Purchase #3	$211.59	12.553%	$238.1509	$238.15	$238.15	$238.20
Purchase #4	$62.38	10.571%	$68.9742	$68.97	$68.95	$69.00
Purchase #5	$133.33	9.457%	$145.939	$145.94	$145.95	$145.90
Purchase #6	$48.45	13.252%	$54.8706	$54.87	$54.85	$54.90
Purchase #7	$48.52	12.510%	$54.5899	$54.59	$54.60	$54.60
7 purchase totals =	$714.24		$786.3658	$786.36	$786.35	$786.50