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	$205.57	8.280%	$222.5912	$222.59	$222.60	$222.60
Purchase #2	$110.93	3.118%	$114.3888	$114.39	$114.40	$114.40
Purchase #3	$90.38	10.325%	$99.7117	$99.71	$99.70	$99.70
Purchase #4	$90.83	3.552%	$94.0563	$94.06	$94.05	$94.10
Purchase #5	$94.27	11.847%	$105.4382	$105.44	$105.45	$105.40
Purchase #6	$39.52	12.481%	$44.4525	$44.45	$44.45	$44.50
Purchase #7	$56.39	13.621%	$64.0709	$64.07	$64.05	$64.10
7 purchase totals =	$687.89		$744.7096	$744.71	$744.70	$744.80