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	$94.53	11.667%	$105.5588	$105.56	$105.55	$105.60
Purchase #2	$18.56	13.667%	$21.0966	$21.10	$21.10	$21.10
Purchase #3	$149.63	7.669%	$161.1051	$161.11	$161.10	$161.10
Purchase #4	$217.58	11.102%	$241.7357	$241.74	$241.75	$241.70
Purchase #5	$125.63	10.333%	$138.6113	$138.61	$138.60	$138.60
Purchase #6	$79.64	12.386%	$89.5042	$89.50	$89.50	$89.50
Purchase #7	$117.32	3.492%	$121.4168	$121.42	$121.40	$121.40
7 purchase totals =	$802.89		$879.0285	$879.04	$879.00	$879.00