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	$104.54	3.620%	$108.3243	$108.32	$108.30	$108.30
Purchase #2	$141.45	11.816%	$158.1637	$158.16	$158.15	$158.20
Purchase #3	$235.37	10.313%	$259.6437	$259.64	$259.65	$259.60
Purchase #4	$63.28	7.376%	$67.9475	$67.95	$67.95	$67.90
Purchase #5	$89.53	12.734%	$100.9308	$100.93	$100.95	$100.90
Purchase #6	$70.53	7.845%	$76.0631	$76.06	$76.05	$76.10
Purchase #7	$213.82	6.398%	$227.5002	$227.50	$227.50	$227.50
7 purchase totals =	$918.52		$998.5733	$998.56	$998.55	$998.50