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	$10.40	12.114%	$11.6599	$11.66	$11.65	$11.70
Purchase #2	$55.76	13.839%	$63.4766	$63.48	$63.50	$63.50
Purchase #3	$91.27	9.250%	$99.7125	$99.71	$99.70	$99.70
Purchase #4	$142.92	5.854%	$151.2865	$151.29	$151.30	$151.30
Purchase #5	$26.67	6.403%	$28.3777	$28.38	$28.40	$28.40
Purchase #6	$64.28	13.128%	$72.7187	$72.72	$72.70	$72.70
Purchase #7	$233.45	11.193%	$259.5801	$259.58	$259.60	$259.60
7 purchase totals =	$624.75		$686.8120	$686.82	$686.85	$686.90