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	$13.39	12.210%	$15.0249	$15.02	$15.00	$15.00
Purchase #2	$60.42	9.668%	$66.2614	$66.26	$66.25	$66.30
Purchase #3	$59.83	5.748%	$63.269	$63.27	$63.25	$63.30
Purchase #4	$119.81	7.438%	$128.7215	$128.72	$128.70	$128.70
Purchase #5	$48.37	12.792%	$54.5575	$54.56	$54.55	$54.60
Purchase #6	$54.55	4.608%	$57.0637	$57.06	$57.05	$57.10
Purchase #7	$81.48	10.645%	$90.1535	$90.15	$90.15	$90.20
7 purchase totals =	$437.85		$475.0515	$475.04	$474.95	$475.20