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	$172.76	9.632%	$189.4002	$189.40	$189.40	$189.40
Purchase #2	$169.40	5.647%	$178.966	$178.97	$178.95	$179.00
Purchase #3	$220.52	6.381%	$234.5914	$234.59	$234.60	$234.60
Purchase #4	$85.87	5.741%	$90.7998	$90.80	$90.80	$90.80
Purchase #5	$171.75	12.635%	$193.4506	$193.45	$193.45	$193.50
Purchase #6	$130.69	6.817%	$139.5991	$139.60	$139.60	$139.60
Purchase #7	$47.73	10.722%	$52.8476	$52.85	$52.85	$52.80
7 purchase totals =	$998.72		$1,079.6547	$1,079.66	$1,079.65	$1,079.70