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	$136.98	10.562%	$151.4478	$151.45	$151.45	$151.40
Purchase #2	$19.77	7.507%	$21.2541	$21.25	$21.25	$21.30
Purchase #3	$90.25	11.637%	$100.7524	$100.75	$100.75	$100.80
Purchase #4	$29.53	4.460%	$30.847	$30.85	$30.85	$30.80
Purchase #5	$26.32	8.567%	$28.5748	$28.57	$28.55	$28.60
Purchase #6	$132.41	9.406%	$144.8645	$144.86	$144.85	$144.90
Purchase #7	$100.62	7.693%	$108.3607	$108.36	$108.35	$108.40
7 purchase totals =	$535.88		$586.1013	$586.09	$586.05	$586.20