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	$139.89	13.668%	$159.0102	$159.01	$159.00	$159.00
Purchase #2	$129.77	12.792%	$146.3702	$146.37	$146.35	$146.40
Purchase #3	$138.65	12.861%	$156.4818	$156.48	$156.50	$156.50
Purchase #4	$42.83	6.307%	$45.5313	$45.53	$45.55	$45.50
Purchase #5	$43.78	12.705%	$49.3422	$49.34	$49.35	$49.30
Purchase #6	$110.86	6.757%	$118.3508	$118.35	$118.35	$118.40
Purchase #7	$39.82	8.382%	$43.1577	$43.16	$43.15	$43.20
7 purchase totals =	$645.60		$718.2442	$718.24	$718.25	$718.30