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	$72.91	10.577%	$80.6217	$80.62	$80.60	$80.60
Purchase #2	$50.68	6.560%	$54.0046	$54.00	$54.00	$54.00
Purchase #3	$44.41	5.603%	$46.8983	$46.90	$46.90	$46.90
Purchase #4	$37.78	7.492%	$40.6105	$40.61	$40.60	$40.60
Purchase #5	$190.36	8.476%	$206.4949	$206.49	$206.50	$206.50
Purchase #6	$241.25	12.538%	$271.4979	$271.50	$271.50	$271.50
Purchase #7	$249.64	11.375%	$278.0366	$278.04	$278.05	$278.00
7 purchase totals =	$887.03		$978.1645	$978.16	$978.15	$978.10