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	$10.57	13.730%	$12.0213	$12.02	$12.00	$12.00
Purchase #2	$230.58	13.715%	$262.204	$262.20	$262.20	$262.20
Purchase #3	$206.43	6.215%	$219.2596	$219.26	$219.25	$219.30
Purchase #4	$34.91	8.423%	$37.8505	$37.85	$37.85	$37.90
Purchase #5	$137.89	4.319%	$143.8455	$143.85	$143.85	$143.80
Purchase #6	$52.37	4.567%	$54.7617	$54.76	$54.75	$54.80
Purchase #7	$12.76	8.541%	$13.8498	$13.85	$13.85	$13.80
7 purchase totals =	$685.51		$743.7924	$743.79	$743.75	$743.80