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	$132.85	5.310%	$139.9043	$139.90	$139.90	$139.90
Purchase #2	$167.32	13.778%	$190.3733	$190.37	$190.35	$190.40
Purchase #3	$216.37	6.727%	$230.9252	$230.93	$230.95	$230.90
Purchase #4	$157.89	10.330%	$174.2	$174.20	$174.20	$174.20
Purchase #5	$72.60	11.146%	$80.692	$80.69	$80.70	$80.70
Purchase #6	$87.87	5.463%	$92.6703	$92.67	$92.65	$92.70
Purchase #7	$143.73	10.667%	$159.0617	$159.06	$159.05	$159.10
7 purchase totals =	$978.63		$1,067.8268	$1,067.82	$1,067.80	$1,067.90