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	$48.89	3.196%	$50.4525	$50.45	$50.45	$50.50
Purchase #2	$116.32	10.755%	$128.8302	$128.83	$128.85	$128.80
Purchase #3	$245.35	3.388%	$253.6625	$253.66	$253.65	$253.70
Purchase #4	$202.46	12.418%	$227.6015	$227.60	$227.60	$227.60
Purchase #5	$17.78	4.794%	$18.6324	$18.63	$18.65	$18.60
Purchase #6	$22.99	8.236%	$24.8835	$24.88	$24.90	$24.90
Purchase #7	$82.70	11.271%	$92.0211	$92.02	$92.00	$92.00
7 purchase totals =	$736.49		$796.0837	$796.07	$796.10	$796.10