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	$55.86	13.256%	$63.2648	$63.26	$63.25	$63.30
Purchase #2	$105.37	13.668%	$119.772	$119.77	$119.75	$119.80
Purchase #3	$64.88	4.693%	$67.9248	$67.92	$67.90	$67.90
Purchase #4	$44.85	9.383%	$49.0583	$49.06	$49.05	$49.10
Purchase #5	$126.82	4.619%	$132.6778	$132.68	$132.70	$132.70
Purchase #6	$59.79	4.521%	$62.4931	$62.49	$62.50	$62.50
Purchase #7	$40.66	3.190%	$41.9571	$41.96	$41.95	$42.00
7 purchase totals =	$498.23		$537.1479	$537.14	$537.10	$537.30