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	$43.81	13.423%	$49.6906	$49.69	$49.70	$49.70
Purchase #2	$152.46	4.603%	$159.4777	$159.48	$159.50	$159.50
Purchase #3	$38.44	3.622%	$39.8323	$39.83	$39.85	$39.80
Purchase #4	$151.49	13.598%	$172.0896	$172.09	$172.10	$172.10
Purchase #5	$184.85	3.240%	$190.8391	$190.84	$190.85	$190.80
Purchase #6	$202.92	8.664%	$220.501	$220.50	$220.50	$220.50
Purchase #7	$154.45	8.384%	$167.3991	$167.40	$167.40	$167.40
7 purchase totals =	$928.42		$999.8294	$999.83	$999.90	$999.80