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	$185.54	13.122%	$209.8866	$209.89	$209.90	$209.90
Purchase #2	$161.35	10.590%	$178.437	$178.44	$178.45	$178.40
Purchase #3	$143.69	7.711%	$154.7699	$154.77	$154.75	$154.80
Purchase #4	$223.84	3.251%	$231.117	$231.12	$231.10	$231.10
Purchase #5	$35.54	5.788%	$37.5971	$37.60	$37.60	$37.60
Purchase #6	$13.89	8.633%	$15.0891	$15.09	$15.10	$15.10
Purchase #7	$138.34	13.406%	$156.8859	$156.89	$156.90	$156.90
7 purchase totals =	$902.19		$983.7826	$983.80	$983.80	$983.80