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	$61.77	6.692%	$65.9036	$65.90	$65.90	$65.90
Purchase #2	$21.51	8.166%	$23.2665	$23.27	$23.25	$23.30
Purchase #3	$130.39	9.590%	$142.8944	$142.89	$142.90	$142.90
Purchase #4	$97.47	3.117%	$100.5081	$100.51	$100.50	$100.50
Purchase #5	$137.76	4.698%	$144.232	$144.23	$144.25	$144.20
Purchase #6	$169.65	11.483%	$189.1309	$189.13	$189.15	$189.10
Purchase #7	$163.99	6.338%	$174.3837	$174.38	$174.40	$174.40
7 purchase totals =	$782.54		$840.3192	$840.31	$840.35	$840.30