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	$56.89	6.332%	$60.4923	$60.49	$60.50	$60.50
Purchase #2	$74.98	4.295%	$78.2004	$78.20	$78.20	$78.20
Purchase #3	$110.74	4.796%	$116.0511	$116.05	$116.05	$116.10
Purchase #4	$58.38	9.733%	$64.0621	$64.06	$64.05	$64.10
Purchase #5	$187.35	11.863%	$209.5753	$209.58	$209.60	$209.60
Purchase #6	$217.25	11.212%	$241.6081	$241.61	$241.60	$241.60
Purchase #7	$120.76	6.718%	$128.8727	$128.87	$128.85	$128.90
7 purchase totals =	$826.35		$898.8620	$898.86	$898.85	$899.00