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	$85.26	4.815%	$89.3653	$89.37	$89.35	$89.40
Purchase #2	$32.98	12.153%	$36.9881	$36.99	$37.00	$37.00
Purchase #3	$116.59	10.793%	$129.1736	$129.17	$129.15	$129.20
Purchase #4	$41.89	6.286%	$44.5232	$44.52	$44.50	$44.50
Purchase #5	$37.87	6.350%	$40.2747	$40.27	$40.25	$40.30
Purchase #6	$99.84	9.754%	$109.5784	$109.58	$109.60	$109.60
Purchase #7	$139.76	3.668%	$144.8864	$144.89	$144.90	$144.90
7 purchase totals =	$554.19		$594.7897	$594.79	$594.75	$594.90