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	$5.88	12.548%	$6.6178	$6.62	$6.60	$6.60
Purchase #2	$190.87	12.604%	$214.9273	$214.93	$214.95	$214.90
Purchase #3	$150.84	11.709%	$168.5019	$168.50	$168.50	$168.50
Purchase #4	$221.94	5.613%	$234.3975	$234.40	$234.40	$234.40
Purchase #5	$143.28	4.756%	$150.0944	$150.09	$150.10	$150.10
Purchase #6	$31.65	12.865%	$35.7218	$35.72	$35.70	$35.70
Purchase #7	$169.40	13.524%	$192.3097	$192.31	$192.30	$192.30
7 purchase totals =	$913.86		$1,002.5704	$1,002.57	$1,002.55	$1,002.50