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	$21.34	13.795%	$24.2839	$24.28	$24.30	$24.30
Purchase #2	$169.52	3.413%	$175.3057	$175.31	$175.30	$175.30
Purchase #3	$111.34	11.609%	$124.2655	$124.27	$124.25	$124.30
Purchase #4	$82.55	12.145%	$92.5757	$92.58	$92.60	$92.60
Purchase #5	$167.50	3.842%	$173.9354	$173.94	$173.95	$173.90
Purchase #6	$11.34	5.306%	$11.9417	$11.94	$11.95	$11.90
Purchase #7	$58.56	9.433%	$64.084	$64.08	$64.10	$64.10
7 purchase totals =	$622.15		$666.3919	$666.40	$666.45	$666.40