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	$20.36	3.844%	$21.1426	$21.14	$21.15	$21.10
Purchase #2	$106.86	11.388%	$119.0292	$119.03	$119.05	$119.00
Purchase #3	$173.97	9.522%	$190.5354	$190.54	$190.55	$190.50
Purchase #4	$54.40	3.759%	$56.4449	$56.44	$56.45	$56.40
Purchase #5	$208.45	7.703%	$224.5069	$224.51	$224.50	$224.50
Purchase #6	$248.30	9.644%	$272.2461	$272.25	$272.25	$272.20
Purchase #7	$209.55	6.248%	$222.6427	$222.64	$222.65	$222.60
7 purchase totals =	$1,021.89		$1,106.5478	$1,106.55	$1,106.60	$1,106.30