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	$137.78	9.514%	$150.8884	$150.89	$150.90	$150.90
Purchase #2	$226.98	13.616%	$257.8856	$257.89	$257.90	$257.90
Purchase #3	$212.37	10.103%	$233.8257	$233.83	$233.85	$233.80
Purchase #4	$114.61	11.219%	$127.4681	$127.47	$127.45	$127.50
Purchase #5	$239.73	5.777%	$253.5792	$253.58	$253.60	$253.60
Purchase #6	$74.50	5.507%	$78.6027	$78.60	$78.60	$78.60
Purchase #7	$163.28	6.733%	$174.2736	$174.27	$174.25	$174.30
7 purchase totals =	$1,169.25		$1,276.5233	$1,276.53	$1,276.55	$1,276.60