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	$82.99	7.284%	$89.035	$89.04	$89.05	$89.00
Purchase #2	$45.82	12.513%	$51.5535	$51.55	$51.55	$51.60
Purchase #3	$41.84	5.813%	$44.2722	$44.27	$44.25	$44.30
Purchase #4	$218.38	9.383%	$238.8706	$238.87	$238.85	$238.90
Purchase #5	$227.39	7.495%	$244.4329	$244.43	$244.45	$244.40
Purchase #6	$62.95	12.115%	$70.5764	$70.58	$70.60	$70.60
Purchase #7	$57.80	13.856%	$65.8088	$65.81	$65.80	$65.80
7 purchase totals =	$737.17		$804.5494	$804.55	$804.55	$804.60