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	$238.36	9.754%	$261.6096	$261.61	$261.60	$261.60
Purchase #2	$94.77	10.364%	$104.592	$104.59	$104.60	$104.60
Purchase #3	$145.43	9.116%	$158.6874	$158.69	$158.70	$158.70
Purchase #4	$112.97	7.795%	$121.776	$121.78	$121.80	$121.80
Purchase #5	$54.99	8.119%	$59.4546	$59.45	$59.45	$59.50
Purchase #6	$41.42	9.861%	$45.5044	$45.50	$45.50	$45.50
Purchase #7	$84.77	5.688%	$89.5917	$89.59	$89.60	$89.60
7 purchase totals =	$772.71		$841.2157	$841.21	$841.25	$841.30