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	$16.59	7.498%	$17.8339	$17.83	$17.85	$17.80
Purchase #2	$11.72	6.266%	$12.4544	$12.45	$12.45	$12.50
Purchase #3	$85.46	8.125%	$92.4036	$92.40	$92.40	$92.40
Purchase #4	$50.51	11.569%	$56.3535	$56.35	$56.35	$56.40
Purchase #5	$90.58	5.680%	$95.7249	$95.72	$95.70	$95.70
Purchase #6	$93.41	12.814%	$105.3796	$105.38	$105.40	$105.40
Purchase #7	$222.34	11.357%	$247.5912	$247.59	$247.60	$247.60
7 purchase totals =	$570.61		$627.7411	$627.72	$627.75	$627.80