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	$51.45	10.340%	$56.7699	$56.77	$56.75	$56.80
Purchase #2	$49.76	12.553%	$56.0064	$56.01	$56.00	$56.00
Purchase #3	$146.94	6.475%	$156.4544	$156.45	$156.45	$156.50
Purchase #4	$43.96	11.618%	$49.0673	$49.07	$49.05	$49.10
Purchase #5	$59.58	11.681%	$66.5395	$66.54	$66.55	$66.50
Purchase #6	$168.50	6.481%	$179.4205	$179.42	$179.40	$179.40
Purchase #7	$100.99	8.163%	$109.2338	$109.23	$109.25	$109.20
7 purchase totals =	$621.18		$673.4918	$673.49	$673.45	$673.50