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	$121.37	5.489%	$128.032	$128.03	$128.05	$128.00
Purchase #2	$43.54	10.783%	$48.2349	$48.23	$48.25	$48.20
Purchase #3	$89.54	7.764%	$96.4919	$96.49	$96.50	$96.50
Purchase #4	$9.28	13.563%	$10.5386	$10.54	$10.55	$10.50
Purchase #5	$70.42	5.439%	$74.2501	$74.25	$74.25	$74.30
Purchase #6	$102.94	11.182%	$114.4508	$114.45	$114.45	$114.50
Purchase #7	$25.36	13.451%	$28.7712	$28.77	$28.75	$28.80
7 purchase totals =	$462.45		$500.7695	$500.76	$500.80	$500.80