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	$78.62	13.260%	$89.045	$89.05	$89.05	$89.00
Purchase #2	$61.99	7.257%	$66.4886	$66.49	$66.50	$66.50
Purchase #3	$105.72	6.577%	$112.6732	$112.67	$112.65	$112.70
Purchase #4	$81.81	4.585%	$85.561	$85.56	$85.55	$85.60
Purchase #5	$138.39	13.612%	$157.2276	$157.23	$157.25	$157.20
Purchase #6	$189.96	8.119%	$205.3829	$205.38	$205.40	$205.40
Purchase #7	$52.60	3.545%	$54.4647	$54.46	$54.45	$54.50
7 purchase totals =	$709.09		$770.8430	$770.84	$770.85	$770.90