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	$118.25	4.426%	$123.4837	$123.48	$123.50	$123.50
Purchase #2	$243.70	11.847%	$272.5711	$272.57	$272.55	$272.60
Purchase #3	$114.78	13.716%	$130.5232	$130.52	$130.50	$130.50
Purchase #4	$174.27	10.121%	$191.9079	$191.91	$191.90	$191.90
Purchase #5	$107.71	13.737%	$122.5061	$122.51	$122.50	$122.50
Purchase #6	$208.91	10.522%	$230.8915	$230.89	$230.90	$230.90
Purchase #7	$109.92	5.860%	$116.3613	$116.36	$116.35	$116.40
7 purchase totals =	$1,077.54		$1,188.2448	$1,188.24	$1,188.20	$1,188.30