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	$42.46	9.404%	$46.4529	$46.45	$46.45	$46.50
Purchase #2	$37.68	12.149%	$42.2577	$42.26	$42.25	$42.30
Purchase #3	$237.64	7.605%	$255.7125	$255.71	$255.70	$255.70
Purchase #4	$88.89	13.710%	$101.0768	$101.08	$101.10	$101.10
Purchase #5	$236.31	8.861%	$257.2494	$257.25	$257.25	$257.20
Purchase #6	$53.86	9.766%	$59.12	$59.12	$59.10	$59.10
Purchase #7	$47.31	5.307%	$49.8207	$49.82	$49.80	$49.80
7 purchase totals =	$744.15		$811.6900	$811.69	$811.65	$811.70