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	$37.84	5.363%	$39.8694	$39.87	$39.85	$39.90
Purchase #2	$140.86	9.659%	$154.4657	$154.47	$154.45	$154.50
Purchase #3	$196.89	8.372%	$213.3736	$213.37	$213.35	$213.40
Purchase #4	$33.34	3.796%	$34.6056	$34.61	$34.60	$34.60
Purchase #5	$176.71	7.853%	$190.587	$190.59	$190.60	$190.60
Purchase #6	$147.42	4.359%	$153.846	$153.85	$153.85	$153.80
Purchase #7	$19.98	12.466%	$22.4707	$22.47	$22.45	$22.50
7 purchase totals =	$753.04		$809.2180	$809.23	$809.15	$809.30