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	$102.32	9.351%	$111.8879	$111.89	$111.90	$111.90
Purchase #2	$51.34	13.871%	$58.4614	$58.46	$58.45	$58.50
Purchase #3	$104.32	9.602%	$114.3368	$114.34	$114.35	$114.30
Purchase #4	$119.46	6.837%	$127.6275	$127.63	$127.65	$127.60
Purchase #5	$57.82	8.638%	$62.8145	$62.81	$62.80	$62.80
Purchase #6	$86.36	10.265%	$95.2249	$95.22	$95.20	$95.20
Purchase #7	$19.72	11.239%	$21.9363	$21.94	$21.95	$21.90
7 purchase totals =	$541.34		$592.2893	$592.29	$592.30	$592.20