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	$229.45	12.783%	$258.7806	$258.78	$258.80	$258.80
Purchase #2	$10.97	4.664%	$11.4816	$11.48	$11.50	$11.50
Purchase #3	$89.35	12.461%	$100.4839	$100.48	$100.50	$100.50
Purchase #4	$224.68	7.672%	$241.9174	$241.92	$241.90	$241.90
Purchase #5	$175.77	6.758%	$187.6485	$187.65	$187.65	$187.60
Purchase #6	$33.31	7.848%	$35.9242	$35.92	$35.90	$35.90
Purchase #7	$79.86	8.865%	$86.9396	$86.94	$86.95	$86.90
7 purchase totals =	$843.39		$923.1758	$923.17	$923.20	$923.10