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	$39.83	13.271%	$45.1158	$45.12	$45.10	$45.10
Purchase #2	$129.52	9.863%	$142.2946	$142.29	$142.30	$142.30
Purchase #3	$76.77	11.498%	$85.597	$85.60	$85.60	$85.60
Purchase #4	$144.64	5.693%	$152.8744	$152.87	$152.85	$152.90
Purchase #5	$117.99	6.763%	$125.9697	$125.97	$125.95	$126.00
Purchase #6	$112.69	3.533%	$116.6713	$116.67	$116.65	$116.70
Purchase #7	$140.70	9.388%	$153.9089	$153.91	$153.90	$153.90
7 purchase totals =	$762.14		$822.4317	$822.43	$822.35	$822.50