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	$95.71	4.237%	$99.7652	$99.77	$99.75	$99.80
Purchase #2	$57.53	10.434%	$63.5327	$63.53	$63.55	$63.50
Purchase #3	$83.57	13.171%	$94.577	$94.58	$94.60	$94.60
Purchase #4	$138.80	11.693%	$155.0299	$155.03	$155.05	$155.00
Purchase #5	$119.89	10.356%	$132.3058	$132.31	$132.30	$132.30
Purchase #6	$62.33	11.653%	$69.5933	$69.59	$69.60	$69.60
Purchase #7	$211.72	6.313%	$225.0859	$225.09	$225.10	$225.10
7 purchase totals =	$769.55		$839.8898	$839.90	$839.95	$839.90