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	$49.86	13.750%	$56.7158	$56.72	$56.70	$56.70
Purchase #2	$59.76	6.199%	$63.4645	$63.46	$63.45	$63.50
Purchase #3	$230.42	13.536%	$261.6097	$261.61	$261.60	$261.60
Purchase #4	$53.88	10.378%	$59.4717	$59.47	$59.45	$59.50
Purchase #5	$224.82	10.478%	$248.3766	$248.38	$248.40	$248.40
Purchase #6	$139.37	3.679%	$144.4974	$144.50	$144.50	$144.50
Purchase #7	$136.75	6.657%	$145.8534	$145.85	$145.85	$145.90
7 purchase totals =	$894.86		$979.9891	$979.99	$979.95	$980.10