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	$56.53	9.326%	$61.802	$61.80	$61.80	$61.80
Purchase #2	$9.97	13.797%	$11.3456	$11.35	$11.35	$11.30
Purchase #3	$92.47	8.718%	$100.5315	$100.53	$100.55	$100.50
Purchase #4	$95.44	10.680%	$105.633	$105.63	$105.65	$105.60
Purchase #5	$112.78	10.705%	$124.8531	$124.85	$124.85	$124.90
Purchase #6	$41.86	8.228%	$45.3042	$45.30	$45.30	$45.30
Purchase #7	$45.45	7.580%	$48.8951	$48.90	$48.90	$48.90
7 purchase totals =	$454.50		$498.3645	$498.36	$498.40	$498.30