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	$206.77	11.365%	$230.2694	$230.27	$230.25	$230.30
Purchase #2	$191.86	4.388%	$200.2788	$200.28	$200.30	$200.30
Purchase #3	$167.81	13.441%	$190.3653	$190.37	$190.35	$190.40
Purchase #4	$196.54	10.532%	$217.2396	$217.24	$217.25	$217.20
Purchase #5	$81.33	11.713%	$90.8562	$90.86	$90.85	$90.90
Purchase #6	$74.50	12.599%	$83.8863	$83.89	$83.90	$83.90
Purchase #7	$83.95	4.477%	$87.7084	$87.71	$87.70	$87.70
7 purchase totals =	$1,002.76		$1,100.6040	$1,100.62	$1,100.60	$1,100.70