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	$94.52	5.863%	$100.0617	$100.06	$100.05	$100.10
Purchase #2	$105.78	3.852%	$109.8546	$109.85	$109.85	$109.90
Purchase #3	$104.70	7.679%	$112.7399	$112.74	$112.75	$112.70
Purchase #4	$83.59	6.804%	$89.2775	$89.28	$89.30	$89.30
Purchase #5	$108.61	5.285%	$114.35	$114.35	$114.35	$114.40
Purchase #6	$21.72	9.366%	$23.7543	$23.75	$23.75	$23.80
Purchase #7	$8.33	8.415%	$9.031	$9.03	$9.05	$9.00
7 purchase totals =	$527.25		$559.0690	$559.06	$559.10	$559.20