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	$229.40	12.672%	$258.4696	$258.47	$258.45	$258.50
Purchase #2	$78.87	9.548%	$86.4005	$86.40	$86.40	$86.40
Purchase #3	$94.81	4.116%	$98.7124	$98.71	$98.70	$98.70
Purchase #4	$245.79	11.125%	$273.1341	$273.13	$273.15	$273.10
Purchase #5	$105.49	5.844%	$111.6548	$111.65	$111.65	$111.70
Purchase #6	$102.77	13.272%	$116.4096	$116.41	$116.40	$116.40
Purchase #7	$35.80	10.306%	$39.4895	$39.49	$39.50	$39.50
7 purchase totals =	$892.93		$984.2705	$984.26	$984.25	$984.30