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	$230.90	10.659%	$255.5116	$255.51	$255.50	$255.50
Purchase #2	$154.70	7.284%	$165.9683	$165.97	$165.95	$166.00
Purchase #3	$80.82	9.519%	$88.5133	$88.51	$88.50	$88.50
Purchase #4	$118.81	4.791%	$124.5022	$124.50	$124.50	$124.50
Purchase #5	$239.51	8.196%	$259.1402	$259.14	$259.15	$259.10
Purchase #6	$53.78	6.359%	$57.1999	$57.20	$57.20	$57.20
Purchase #7	$115.80	4.369%	$120.8593	$120.86	$120.85	$120.90
7 purchase totals =	$994.32		$1,071.6948	$1,071.69	$1,071.65	$1,071.70