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	$242.49	12.864%	$273.6839	$273.68	$273.70	$273.70
Purchase #2	$35.64	12.343%	$40.039	$40.04	$40.05	$40.00
Purchase #3	$243.39	10.870%	$269.8465	$269.85	$269.85	$269.80
Purchase #4	$33.40	9.154%	$36.4574	$36.46	$36.45	$36.50
Purchase #5	$206.89	5.720%	$218.7241	$218.72	$218.70	$218.70
Purchase #6	$94.80	4.779%	$99.3305	$99.33	$99.35	$99.30
Purchase #7	$19.51	10.538%	$21.566	$21.57	$21.55	$21.60
7 purchase totals =	$876.12		$959.6474	$959.65	$959.65	$959.60