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	$80.73	9.566%	$88.4526	$88.45	$88.45	$88.50
Purchase #2	$240.64	13.279%	$272.5946	$272.59	$272.60	$272.60
Purchase #3	$135.65	7.423%	$145.7193	$145.72	$145.70	$145.70
Purchase #4	$43.94	11.145%	$48.8371	$48.84	$48.85	$48.80
Purchase #5	$84.49	10.517%	$93.3758	$93.38	$93.40	$93.40
Purchase #6	$200.63	10.730%	$222.1576	$222.16	$222.15	$222.20
Purchase #7	$63.85	11.174%	$70.9846	$70.98	$71.00	$71.00
7 purchase totals =	$849.93		$942.1216	$942.12	$942.15	$942.20