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	$8.62	6.153%	$9.1504	$9.15	$9.15	$9.20
Purchase #2	$59.72	11.389%	$66.5215	$66.52	$66.50	$66.50
Purchase #3	$212.48	12.236%	$238.4791	$238.48	$238.50	$238.50
Purchase #4	$243.36	6.166%	$258.3656	$258.37	$258.35	$258.40
Purchase #5	$46.27	9.256%	$50.5528	$50.55	$50.55	$50.60
Purchase #6	$167.50	4.716%	$175.3993	$175.40	$175.40	$175.40
Purchase #7	$34.69	7.384%	$37.2515	$37.25	$37.25	$37.30
7 purchase totals =	$772.64		$835.7202	$835.72	$835.70	$835.90