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	$249.94	12.632%	$281.5124	$281.51	$281.50	$281.50
Purchase #2	$86.45	7.342%	$92.7972	$92.80	$92.80	$92.80
Purchase #3	$240.64	5.851%	$254.7198	$254.72	$254.70	$254.70
Purchase #4	$173.83	9.642%	$190.5907	$190.59	$190.60	$190.60
Purchase #5	$126.58	8.104%	$136.838	$136.84	$136.85	$136.80
Purchase #6	$155.51	6.471%	$165.5731	$165.57	$165.55	$165.60
Purchase #7	$151.77	9.684%	$166.4674	$166.47	$166.45	$166.50
7 purchase totals =	$1,184.72		$1,288.4986	$1,288.50	$1,288.45	$1,288.50