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	$48.80	4.572%	$51.0311	$51.03	$51.05	$51.00
Purchase #2	$54.83	12.452%	$61.6574	$61.66	$61.65	$61.70
Purchase #3	$214.87	12.375%	$241.4602	$241.46	$241.45	$241.50
Purchase #4	$156.38	8.223%	$169.2391	$169.24	$169.25	$169.20
Purchase #5	$43.37	10.138%	$47.7669	$47.77	$47.75	$47.80
Purchase #6	$143.74	5.673%	$151.8944	$151.89	$151.90	$151.90
Purchase #7	$172.77	9.168%	$188.6096	$188.61	$188.60	$188.60
7 purchase totals =	$834.76		$911.6587	$911.66	$911.65	$911.70