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	$54.28	10.435%	$59.9441	$59.94	$59.95	$59.90
Purchase #2	$81.87	4.367%	$85.4453	$85.45	$85.45	$85.40
Purchase #3	$214.64	10.700%	$237.6065	$237.61	$237.60	$237.60
Purchase #4	$72.30	3.259%	$74.6563	$74.66	$74.65	$74.70
Purchase #5	$234.71	13.380%	$266.1142	$266.11	$266.10	$266.10
Purchase #6	$57.69	3.869%	$59.922	$59.92	$59.90	$59.90
Purchase #7	$55.92	12.750%	$63.0498	$63.05	$63.05	$63.00
7 purchase totals =	$771.41		$846.7382	$846.74	$846.70	$846.60