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	$37.62	11.793%	$42.0565	$42.06	$42.05	$42.10
Purchase #2	$74.57	5.478%	$78.6549	$78.65	$78.65	$78.70
Purchase #3	$175.42	10.429%	$193.7146	$193.71	$193.70	$193.70
Purchase #4	$66.57	8.863%	$72.4701	$72.47	$72.45	$72.50
Purchase #5	$225.42	13.127%	$255.0109	$255.01	$255.00	$255.00
Purchase #6	$126.45	6.264%	$134.3708	$134.37	$134.35	$134.40
Purchase #7	$87.80	9.165%	$95.8469	$95.85	$95.85	$95.80
7 purchase totals =	$793.85		$872.1247	$872.12	$872.05	$872.20