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	$109.47	6.388%	$116.4629	$116.46	$116.45	$116.50
Purchase #2	$105.77	6.288%	$112.4208	$112.42	$112.40	$112.40
Purchase #3	$106.59	4.762%	$111.6658	$111.67	$111.65	$111.70
Purchase #4	$207.26	3.360%	$214.2239	$214.22	$214.20	$214.20
Purchase #5	$72.37	12.257%	$81.2404	$81.24	$81.25	$81.20
Purchase #6	$137.46	6.326%	$146.1557	$146.16	$146.15	$146.20
Purchase #7	$59.69	12.273%	$67.0158	$67.02	$67.00	$67.00
7 purchase totals =	$798.61		$849.1853	$849.19	$849.10	$849.20