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	$175.94	8.187%	$190.3442	$190.34	$190.35	$190.30
Purchase #2	$136.90	13.241%	$155.0269	$155.03	$155.05	$155.00
Purchase #3	$130.39	10.372%	$143.9141	$143.91	$143.90	$143.90
Purchase #4	$161.77	7.395%	$173.7329	$173.73	$173.75	$173.70
Purchase #5	$81.27	13.694%	$92.3991	$92.40	$92.40	$92.40
Purchase #6	$53.28	11.306%	$59.3038	$59.30	$59.30	$59.30
Purchase #7	$101.66	3.137%	$104.8491	$104.85	$104.85	$104.80
7 purchase totals =	$841.21		$919.5701	$919.56	$919.60	$919.40