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	$27.27	8.540%	$29.5989	$29.60	$29.60	$29.60
Purchase #2	$228.97	10.646%	$253.3461	$253.35	$253.35	$253.30
Purchase #3	$34.94	7.641%	$37.6098	$37.61	$37.60	$37.60
Purchase #4	$64.66	9.295%	$70.6701	$70.67	$70.65	$70.70
Purchase #5	$127.59	9.266%	$139.4125	$139.41	$139.40	$139.40
Purchase #6	$49.70	6.421%	$52.8912	$52.89	$52.90	$52.90
Purchase #7	$43.27	13.531%	$49.1249	$49.12	$49.10	$49.10
7 purchase totals =	$576.40		$632.6535	$632.65	$632.60	$632.60