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	$40.97	13.225%	$46.3883	$46.39	$46.40	$46.40
Purchase #2	$26.54	7.172%	$28.4434	$28.44	$28.45	$28.40
Purchase #3	$143.84	6.179%	$152.7279	$152.73	$152.75	$152.70
Purchase #4	$40.68	5.115%	$42.7608	$42.76	$42.75	$42.80
Purchase #5	$132.86	5.697%	$140.429	$140.43	$140.45	$140.40
Purchase #6	$124.76	13.381%	$141.4541	$141.45	$141.45	$141.50
Purchase #7	$81.54	11.536%	$90.9465	$90.95	$90.95	$90.90
7 purchase totals =	$591.19		$643.1500	$643.15	$643.20	$643.10