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	$100.40	10.723%	$111.1659	$111.17	$111.15	$111.20
Purchase #2	$160.40	3.333%	$165.7461	$165.75	$165.75	$165.70
Purchase #3	$72.61	10.792%	$80.4461	$80.45	$80.45	$80.40
Purchase #4	$124.79	12.706%	$140.6458	$140.65	$140.65	$140.60
Purchase #5	$13.68	8.458%	$14.8371	$14.84	$14.85	$14.80
Purchase #6	$12.75	10.575%	$14.0983	$14.10	$14.10	$14.10
Purchase #7	$64.80	3.266%	$66.9164	$66.92	$66.90	$66.90
7 purchase totals =	$549.43		$593.8557	$593.88	$593.85	$593.70