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	$11.32	6.571%	$12.0638	$12.06	$12.05	$12.10
Purchase #2	$145.60	13.637%	$165.4555	$165.46	$165.45	$165.50
Purchase #3	$101.47	4.234%	$105.7662	$105.77	$105.75	$105.80
Purchase #4	$97.53	11.308%	$108.5587	$108.56	$108.55	$108.60
Purchase #5	$30.35	5.474%	$32.0114	$32.01	$32.00	$32.00
Purchase #6	$76.45	5.192%	$80.4193	$80.42	$80.40	$80.40
Purchase #7	$100.57	12.108%	$112.747	$112.75	$112.75	$112.70
7 purchase totals =	$563.29		$617.0219	$617.03	$616.95	$617.10