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	$38.86	4.195%	$40.4902	$40.49	$40.50	$40.50
Purchase #2	$29.98	9.750%	$32.9031	$32.90	$32.90	$32.90
Purchase #3	$90.90	9.229%	$99.2892	$99.29	$99.30	$99.30
Purchase #4	$95.51	12.673%	$107.614	$107.61	$107.60	$107.60
Purchase #5	$169.37	8.558%	$183.8647	$183.86	$183.85	$183.90
Purchase #6	$61.84	6.602%	$65.9227	$65.92	$65.90	$65.90
Purchase #7	$44.76	5.203%	$47.0889	$47.09	$47.10	$47.10
7 purchase totals =	$531.22		$577.1728	$577.16	$577.15	$577.20