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	$55.65	6.711%	$59.3847	$59.38	$59.40	$59.40
Purchase #2	$142.29	8.118%	$153.8411	$153.84	$153.85	$153.80
Purchase #3	$43.39	5.585%	$45.8133	$45.81	$45.80	$45.80
Purchase #4	$83.81	12.708%	$94.4606	$94.46	$94.45	$94.50
Purchase #5	$121.75	8.156%	$131.6799	$131.68	$131.70	$131.70
Purchase #6	$187.28	9.783%	$205.6016	$205.60	$205.60	$205.60
Purchase #7	$187.45	8.738%	$203.8294	$203.83	$203.85	$203.80
7 purchase totals =	$821.62		$894.6106	$894.60	$894.65	$894.60