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	$139.25	6.146%	$147.8083	$147.81	$147.80	$147.80
Purchase #2	$22.60	8.382%	$24.4943	$24.49	$24.50	$24.50
Purchase #3	$26.89	7.172%	$28.8186	$28.82	$28.80	$28.80
Purchase #4	$139.92	12.387%	$157.2519	$157.25	$157.25	$157.30
Purchase #5	$101.57	11.340%	$113.088	$113.09	$113.10	$113.10
Purchase #6	$105.50	5.866%	$111.6886	$111.69	$111.70	$111.70
Purchase #7	$74.29	10.665%	$82.213	$82.21	$82.20	$82.20
7 purchase totals =	$610.02		$665.3627	$665.36	$665.35	$665.40