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	$12.75	5.643%	$13.4695	$13.47	$13.45	$13.50
Purchase #2	$180.38	13.371%	$204.4986	$204.50	$204.50	$204.50
Purchase #3	$220.56	3.414%	$228.0899	$228.09	$228.10	$228.10
Purchase #4	$148.32	11.822%	$165.8544	$165.85	$165.85	$165.90
Purchase #5	$10.51	6.816%	$11.2264	$11.23	$11.25	$11.20
Purchase #6	$84.79	9.255%	$92.6373	$92.64	$92.65	$92.60
Purchase #7	$173.77	13.114%	$196.5582	$196.56	$196.55	$196.60
7 purchase totals =	$831.08		$912.3343	$912.34	$912.35	$912.40