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	$23.65	7.304%	$25.3774	$25.38	$25.40	$25.40
Purchase #2	$217.27	12.609%	$244.6656	$244.67	$244.65	$244.70
Purchase #3	$80.94	10.431%	$89.3829	$89.38	$89.40	$89.40
Purchase #4	$146.89	7.759%	$158.2872	$158.29	$158.30	$158.30
Purchase #5	$80.97	5.338%	$85.2922	$85.29	$85.30	$85.30
Purchase #6	$194.79	11.633%	$217.4499	$217.45	$217.45	$217.40
Purchase #7	$24.96	3.285%	$25.7799	$25.78	$25.80	$25.80
7 purchase totals =	$769.47		$846.2351	$846.24	$846.30	$846.30