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	$108.53	11.373%	$120.8731	$120.87	$120.85	$120.90
Purchase #2	$143.77	11.298%	$160.0131	$160.01	$160.00	$160.00
Purchase #3	$190.25	13.233%	$215.4258	$215.43	$215.45	$215.40
Purchase #4	$83.75	5.816%	$88.6209	$88.62	$88.60	$88.60
Purchase #5	$33.74	11.462%	$37.6073	$37.61	$37.60	$37.60
Purchase #6	$103.61	13.531%	$117.6295	$117.63	$117.65	$117.60
Purchase #7	$109.45	3.357%	$113.1242	$113.12	$113.10	$113.10
7 purchase totals =	$773.10		$853.2939	$853.29	$853.25	$853.20