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	$14.75	7.702%	$15.886	$15.89	$15.90	$15.90
Purchase #2	$30.55	9.722%	$33.5201	$33.52	$33.50	$33.50
Purchase #3	$109.51	9.230%	$119.6178	$119.62	$119.60	$119.60
Purchase #4	$40.59	6.509%	$43.232	$43.23	$43.25	$43.20
Purchase #5	$135.40	6.606%	$144.3445	$144.34	$144.35	$144.30
Purchase #6	$93.80	10.750%	$103.8835	$103.88	$103.90	$103.90
Purchase #7	$99.84	6.827%	$106.6561	$106.66	$106.65	$106.70
7 purchase totals =	$524.44		$567.1400	$567.14	$567.15	$567.10