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	$170.62	11.589%	$190.3932	$190.39	$190.40	$190.40
Purchase #2	$56.81	13.518%	$64.4896	$64.49	$64.50	$64.50
Purchase #3	$43.32	9.773%	$47.5537	$47.55	$47.55	$47.60
Purchase #4	$41.53	4.528%	$43.4105	$43.41	$43.40	$43.40
Purchase #5	$135.79	5.630%	$143.435	$143.44	$143.45	$143.40
Purchase #6	$73.40	6.646%	$78.2782	$78.28	$78.30	$78.30
Purchase #7	$215.53	8.697%	$234.2746	$234.27	$234.25	$234.30
7 purchase totals =	$737.00		$801.8348	$801.83	$801.85	$801.90