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	$179.34	6.247%	$190.5434	$190.54	$190.55	$190.50
Purchase #2	$151.43	13.633%	$172.0745	$172.07	$172.05	$172.10
Purchase #3	$38.92	9.153%	$42.4823	$42.48	$42.50	$42.50
Purchase #4	$63.77	10.169%	$70.2548	$70.25	$70.25	$70.30
Purchase #5	$80.51	5.731%	$85.124	$85.12	$85.10	$85.10
Purchase #6	$112.82	6.540%	$120.1984	$120.20	$120.20	$120.20
Purchase #7	$209.35	11.466%	$233.3541	$233.35	$233.35	$233.40
7 purchase totals =	$836.14		$914.0315	$914.01	$914.00	$914.10