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	$101.78	10.801%	$112.7733	$112.77	$112.75	$112.80
Purchase #2	$39.76	13.565%	$45.1534	$45.15	$45.15	$45.20
Purchase #3	$41.65	11.522%	$46.4489	$46.45	$46.45	$46.40
Purchase #4	$63.81	13.583%	$72.4773	$72.48	$72.50	$72.50
Purchase #5	$41.54	7.357%	$44.5961	$44.60	$44.60	$44.60
Purchase #6	$145.76	7.446%	$156.6133	$156.61	$156.60	$156.60
Purchase #7	$119.77	8.389%	$129.8175	$129.82	$129.80	$129.80
7 purchase totals =	$554.07		$607.8798	$607.88	$607.85	$607.90