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	$171.34	10.127%	$188.6916	$188.69	$188.70	$188.70
Purchase #2	$116.93	10.392%	$129.0814	$129.08	$129.10	$129.10
Purchase #3	$79.26	13.522%	$89.9775	$89.98	$90.00	$90.00
Purchase #4	$67.86	9.708%	$74.4478	$74.45	$74.45	$74.40
Purchase #5	$32.65	10.687%	$36.1393	$36.14	$36.15	$36.10
Purchase #6	$122.54	4.183%	$127.6658	$127.67	$127.65	$127.70
Purchase #7	$65.36	10.179%	$72.013	$72.01	$72.00	$72.00
7 purchase totals =	$655.94		$718.0164	$718.02	$718.05	$718.00