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	$61.39	8.698%	$66.7297	$66.73	$66.75	$66.70
Purchase #2	$86.67	5.688%	$91.5998	$91.60	$91.60	$91.60
Purchase #3	$11.48	11.718%	$12.8252	$12.83	$12.85	$12.80
Purchase #4	$51.58	9.469%	$56.4641	$56.46	$56.45	$56.50
Purchase #5	$176.34	7.512%	$189.5867	$189.59	$189.60	$189.60
Purchase #6	$228.83	11.719%	$255.6466	$255.65	$255.65	$255.60
Purchase #7	$157.84	11.571%	$176.1037	$176.10	$176.10	$176.10
7 purchase totals =	$774.13		$848.9558	$848.96	$849.00	$848.90