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	$11.73	6.273%	$12.4658	$12.47	$12.45	$12.50
Purchase #2	$43.36	9.237%	$47.3652	$47.37	$47.35	$47.40
Purchase #3	$20.53	5.369%	$21.6323	$21.63	$21.65	$21.60
Purchase #4	$69.43	13.383%	$78.7218	$78.72	$78.70	$78.70
Purchase #5	$43.69	5.267%	$45.9912	$45.99	$46.00	$46.00
Purchase #6	$82.60	3.672%	$85.6331	$85.63	$85.65	$85.60
Purchase #7	$205.87	7.863%	$222.0576	$222.06	$222.05	$222.10
7 purchase totals =	$477.21		$513.8670	$513.87	$513.85	$513.90