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	$52.85	7.175%	$56.642	$56.64	$56.65	$56.60
Purchase #2	$51.58	11.270%	$57.3931	$57.39	$57.40	$57.40
Purchase #3	$69.84	4.285%	$72.8326	$72.83	$72.85	$72.80
Purchase #4	$57.26	6.680%	$61.085	$61.09	$61.10	$61.10
Purchase #5	$118.83	11.784%	$132.8329	$132.83	$132.85	$132.80
Purchase #6	$75.82	11.450%	$84.5014	$84.50	$84.50	$84.50
Purchase #7	$92.93	9.643%	$101.8912	$101.89	$101.90	$101.90
7 purchase totals =	$519.11		$567.1782	$567.17	$567.25	$567.10