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	$119.94	7.750%	$129.2354	$129.24	$129.25	$129.20
Purchase #2	$124.82	5.268%	$131.3955	$131.40	$131.40	$131.40
Purchase #3	$29.94	8.222%	$32.4017	$32.40	$32.40	$32.40
Purchase #4	$55.75	13.592%	$63.3275	$63.33	$63.35	$63.30
Purchase #5	$87.75	12.677%	$98.8741	$98.87	$98.85	$98.90
Purchase #6	$87.93	3.387%	$90.9082	$90.91	$90.90	$90.90
Purchase #7	$39.95	9.773%	$43.8543	$43.85	$43.85	$43.90
7 purchase totals =	$546.08		$589.9967	$590.00	$590.00	$590.00