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	$83.27	4.113%	$86.6949	$86.69	$86.70	$86.70
Purchase #2	$159.83	6.687%	$170.5178	$170.52	$170.50	$170.50
Purchase #3	$24.52	11.435%	$27.3239	$27.32	$27.30	$27.30
Purchase #4	$79.46	13.757%	$90.3913	$90.39	$90.40	$90.40
Purchase #5	$106.66	12.559%	$120.0554	$120.06	$120.05	$120.10
Purchase #6	$177.50	10.224%	$195.6476	$195.65	$195.65	$195.60
Purchase #7	$219.80	13.468%	$249.4027	$249.40	$249.40	$249.40
7 purchase totals =	$851.04		$940.0336	$940.03	$940.00	$940.00