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	$241.54	5.788%	$255.5203	$255.52	$255.50	$255.50
Purchase #2	$237.37	6.654%	$253.1646	$253.16	$253.15	$253.20
Purchase #3	$111.95	6.785%	$119.5458	$119.55	$119.55	$119.50
Purchase #4	$94.73	7.406%	$101.7457	$101.75	$101.75	$101.70
Purchase #5	$189.25	9.624%	$207.4634	$207.46	$207.45	$207.50
Purchase #6	$123.88	3.762%	$128.5404	$128.54	$128.55	$128.50
Purchase #7	$139.70	11.828%	$156.2237	$156.22	$156.20	$156.20
7 purchase totals =	$1,138.42		$1,222.2039	$1,222.20	$1,222.15	$1,222.10