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	$178.98	5.496%	$188.8167	$188.82	$188.80	$188.80
Purchase #2	$100.30	4.768%	$105.0823	$105.08	$105.10	$105.10
Purchase #3	$46.80	13.195%	$52.9753	$52.98	$53.00	$53.00
Purchase #4	$233.38	7.578%	$251.0655	$251.07	$251.05	$251.10
Purchase #5	$52.26	4.280%	$54.4967	$54.50	$54.50	$54.50
Purchase #6	$39.90	6.786%	$42.6076	$42.61	$42.60	$42.60
Purchase #7	$108.72	13.273%	$123.1504	$123.15	$123.15	$123.20
7 purchase totals =	$760.34		$818.1945	$818.21	$818.20	$818.30