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	$231.60	10.446%	$255.7929	$255.79	$255.80	$255.80
Purchase #2	$172.49	10.167%	$190.0271	$190.03	$190.05	$190.00
Purchase #3	$219.68	6.635%	$234.2558	$234.26	$234.25	$234.30
Purchase #4	$142.44	9.189%	$155.5288	$155.53	$155.55	$155.50
Purchase #5	$48.81	7.243%	$52.3453	$52.35	$52.35	$52.30
Purchase #6	$109.36	9.188%	$119.408	$119.41	$119.40	$119.40
Purchase #7	$159.52	3.767%	$165.5291	$165.53	$165.55	$165.50
7 purchase totals =	$1,083.90		$1,172.8870	$1,172.90	$1,172.95	$1,172.80