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	$127.25	9.782%	$139.6976	$139.70	$139.70	$139.70
Purchase #2	$79.38	12.152%	$89.0263	$89.03	$89.05	$89.00
Purchase #3	$140.95	12.239%	$158.2009	$158.20	$158.20	$158.20
Purchase #4	$71.87	11.864%	$80.3967	$80.40	$80.40	$80.40
Purchase #5	$73.80	6.585%	$78.6597	$78.66	$78.65	$78.70
Purchase #6	$213.64	6.223%	$226.9348	$226.93	$226.95	$226.90
Purchase #7	$6.81	10.842%	$7.5483	$7.55	$7.55	$7.50
7 purchase totals =	$713.70		$780.4643	$780.47	$780.50	$780.40