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	$17.91	10.114%	$19.7214	$19.72	$19.70	$19.70
Purchase #2	$85.63	4.848%	$89.7813	$89.78	$89.80	$89.80
Purchase #3	$245.57	5.112%	$258.1235	$258.12	$258.10	$258.10
Purchase #4	$103.49	12.619%	$116.5494	$116.55	$116.55	$116.50
Purchase #5	$220.30	13.521%	$250.0868	$250.09	$250.10	$250.10
Purchase #6	$19.74	11.230%	$21.9568	$21.96	$21.95	$22.00
Purchase #7	$143.25	11.249%	$159.3642	$159.36	$159.35	$159.40
7 purchase totals =	$835.89		$915.5834	$915.58	$915.55	$915.60