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	$21.95	11.455%	$24.4644	$24.46	$24.45	$24.50
Purchase #2	$248.33	10.869%	$275.321	$275.32	$275.30	$275.30
Purchase #3	$65.77	11.153%	$73.1053	$73.11	$73.10	$73.10
Purchase #4	$176.40	4.608%	$184.5285	$184.53	$184.55	$184.50
Purchase #5	$15.32	13.235%	$17.3476	$17.35	$17.35	$17.30
Purchase #6	$8.91	13.392%	$10.1032	$10.10	$10.10	$10.10
Purchase #7	$55.46	7.229%	$59.4692	$59.47	$59.45	$59.50
7 purchase totals =	$592.14		$644.3392	$644.34	$644.30	$644.30