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	$246.60	11.829%	$275.7703	$275.77	$275.75	$275.80
Purchase #2	$123.29	9.222%	$134.6598	$134.66	$134.65	$134.70
Purchase #3	$159.63	10.330%	$176.1198	$176.12	$176.10	$176.10
Purchase #4	$69.77	11.799%	$78.0022	$78.00	$78.00	$78.00
Purchase #5	$107.71	3.539%	$111.5219	$111.52	$111.50	$111.50
Purchase #6	$49.26	10.479%	$54.422	$54.42	$54.40	$54.40
Purchase #7	$104.87	13.754%	$119.2938	$119.29	$119.30	$119.30
7 purchase totals =	$861.13		$949.7898	$949.78	$949.70	$949.80