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	$108.49	10.822%	$120.2308	$120.23	$120.25	$120.20
Purchase #2	$20.95	3.162%	$21.6124	$21.61	$21.60	$21.60
Purchase #3	$126.72	9.862%	$139.2171	$139.22	$139.20	$139.20
Purchase #4	$62.47	7.725%	$67.2958	$67.30	$67.30	$67.30
Purchase #5	$98.64	12.661%	$111.1288	$111.13	$111.15	$111.10
Purchase #6	$224.98	6.111%	$238.7285	$238.73	$238.75	$238.70
Purchase #7	$224.71	5.288%	$236.5927	$236.59	$236.60	$236.60
7 purchase totals =	$866.96		$934.8061	$934.81	$934.85	$934.70