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	$27.26	9.178%	$29.7619	$29.76	$29.75	$29.80
Purchase #2	$216.80	10.545%	$239.6616	$239.66	$239.65	$239.70
Purchase #3	$153.29	4.556%	$160.2739	$160.27	$160.25	$160.30
Purchase #4	$245.27	3.221%	$253.1701	$253.17	$253.15	$253.20
Purchase #5	$54.81	9.262%	$59.8865	$59.89	$59.90	$59.90
Purchase #6	$162.39	12.665%	$182.9567	$182.96	$182.95	$183.00
Purchase #7	$109.25	6.604%	$116.4649	$116.46	$116.45	$116.50
7 purchase totals =	$969.07		$1,042.1756	$1,042.17	$1,042.10	$1,042.40